WEATHERGRAM

BOBGRAM issued 5 Feb 2012

2012-02-05T01:44:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 05 February 2012
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina's indicators continue to relax in the atmosphere. The Southern Oscillation Index was 2.3 in late December, and eased to 1.01 during January and is down to 0.79 on 5th February.

A new MJO cycle of enhanced convection is making its way across Australia and the Coral Sea. Near equatorial NW/W winds have broken out across Solomons and are likely to spread towards 180 this week.

The South Pacific Convergence zone SPCZ was very intense last week across Papua New Guinea Vanuatu and Fiji --- this part of the zone had the MOST intense rain on the planet last week according to TRMM—it is less intense further to the southeast across Southern Cooks, and another convergence zone is sitting over French Polynesia. With a new MJO cycle approaching it is likely that we are now moving towards the "business part" of this cyclone season over the next few weeks.

TC JASMINE has formed in the western Coral Sea and is likely to go SE, maybe ESE and cross the Loyalty Island between New Caledonia and Vanuatu on Wed/Thu 8/9 Feb, and then turn south over the 11/12 Fe weekend and weaken.

Fiji Met Service is closely watching a LOW SSW of Fiji that has squally gales over the Tonga area. This system may develop further on Monday as it crosses southern Tonga and then should weaken as it moves off to the southeast.

The low that bothered New Caledonia lat week is still a feature on the weather map, but has lost most of its moisture--- its remains are found near Lord Howe Island at present, and should track southwards and a little eastward across the South Taman Sea over the next few days.

SUBTROPICAL RIDGE STR
A slow-moving high is wandering gradually along 50S to east of NZ and should lose its gripping ridge over North Island from Thu 9 Feb… until Wednesday 8 Feb a moist northerly flow should affect much of NZ.

The next High should spend this week wandering along 40S across the Aussie Bight, with enhanced easterly winds on its northern side along the Aussie Coast. This High should make its way across the south Tasman Sea on the Sat/Sun 11/12 Feb weekend and then onto South Island by Tue 14 Feb.

Between the high pressures to the south and the low pressure to the north--- the Tasman Sea is likely to have mainly easterly winds from Thu 9 to Tue 14 Feb.

Also, these high pressures over NZ should keep other things away for a while.

TASMAN SEA/NZ AREA
The front that went over NZ mid-last-week was followed by a light SE flow, and this filled the NZ area with low cloud. Then that leftover low from New Caledonia made its way to near Lord Howe and combined with a little jetstream making its way around the upper ridge and produced a stream of high cloud that has been making its way across central NZ the last few days. The result has been a messy anticyclone for NZ's Waitangi Day weekend, with lots of cloud and also some damp areas -- some have called it a "filthy high", and it has been a classic illustration of one of my ten reasons for "hating a high".

There is a weak trough and southerly wind change over NZ between the two highs mentioned above… At this stage the timing for this is likely to be on Thu/Fri 9/10 Feb, but nothing dramatic is being indicated in this trough at this stage.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 29 Jan 2012

2012-01-29T00:36:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 29 January 2012
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina's indicators are now levelling out after relaxing over the last month. The Southern Oscillation Index was 2.3 in late December, and eased to 1.16 by 21 Jan, and 1.01 on 29 Jan.

A new MJO cycle of enhanced convection is making its way across Australia and towards the Coral Sea. TC IGGY has been named offshore of West Australia and is likely to wander slowly south this week, hopefully staying well offshore.

The South Pacific Convergence zone SPCZ was very intense last week across Papua New Guinea Vanuatu and Fiji and less intense further to the southeast. It has been carrying rain heavy enough to produce landslides in PNG and Fiji. The zone is shifting around a bit this week but, with a new MJO cycle approaching it is likely that we are now moving towards the "business part" of this cyclone season over the next few weeks. Best to stay put.

It is likely that the LOW now around Vanuatu may deepen over next few days and do a clockwise loop towards New Caledonia by the end of the week. Also another LOW may form in west or central Coral Sea by mid to late week, Avoid.

SUBTROPICAL RIDGE STR
Good news for haymakers over northern NZ. The HIGH that is tonight over the North Tasman Sera should cross the North island on Monday and then be deflected back again by a passing southern front on Tuesday/Wednesday and then fade away in much the same place by the end of the week.

The high that is now in the Aussie bight should stretch eastwards along 50S on Tuesday and build over Chathams on Wednesday and Thursday and then spreading off to the east of NZ. A squash zone of enhanced East to NE winds is likely to remain between this high and the Lows over Coral Sea Vanuatu--- avoid the north Tasman Sea this week.

TASMAN SEA/NZ AREA
A Low over Tasmanian and associated front is expected to slide southeast across the south Tasman Sea during Monday, followed by a weakening trough on Tuesday to Thursday and then a northerly flow on Friday to Saturday. This should help some of the hot air over Australia to reach southern NZ by next weekend.

A cold front is likely to cross southern NZ on Sun/Mon 5/6 Feb, relaxing the winds over New Zealand for their Waitangi Day KIWI day holiday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 22 Jan 2012

2012-01-22T00:28:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 22 January 2012
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina's indicators continue to relax after that late December high. The Southern Oscillation Index was 2.3 in late December, 1.36 on 14 Jan, and 1.16 on 21 Jan,

A new MJO cycle of enhanced convection is appearing in the Indian Ocean and is expected to arrive over western Australian later this week, increasing their risk of tropical cyclone formation. To help these there is a zone of near equatorial westerly winds across Indonesia which is likely to make its way across Papua New Guinea this week.

The South Pacific Convergence zone SPCZ is slowly reforming in the Coral Sea after a few quiet weeks there. It spent last week in a rather scattered fashion mainly along the date line between Tuvalu and Fiji and also across Tokelau then southeastwards to French Polynesia.
A low has formed within the SPCZ to south of Fiji near Minerva and this should wander off to the southeast--- it is likely to encounter some of the cold southerly air that washed over NZ today, this should take place between 30 and 40S near 160W on Tuesday and help form a deepening low that will move off to the south.
There is a risk that another low may form southeast of Fiji on Sat 28 Jan and do a re-enactment of this – moving south and deepening along 170 to 175W next week.

SUBTROPICAL RIDGE STR
A new large High is set to wander slowly south across the Tasman Sea along 40S and fade over North Island on Wed/Thu 25/26 Jan – this is a little to north of the track of the previous high.

The next high is expected to move more quickly than the current high taking the track along 40S across Tasman Sea and Central NZ on Friday 27 to Mon 30 Jan, good timing for Auckland's anniversary day long weekend and regatta.

TASMAN SEA/NZ AREA
Inbetween those two highs there is a transition time for NZ. A cold front fresh from the southern ocean is likely to reach southern NZ late on Thu 26 Jan, and sweep across South then North Islands on Friday and Saturday 27 and 28 Jan. It is associated with a deep southern low which is also likely to bring some heavy swell to southern NZ on Sun/Mon 29/30 Jan.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 15 Jan 212

2012-01-14T22:50:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 15 January 2012
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina's indicators continue to relax after that late December high. The Southern Oscillation Index was 2.3 in late December, 1.79 on 7 Jan and 1.36 on 14 Jan.

Recently a MJO cycle of enhanced convection was apparent over northern Australia but this as weakened away. There may be another forming in the eastern Indian Ocean, and that will take a few weeks to get to the South Pacific. Also there are no sign on any equatorial westerly winds at this stage. So, some of the indicators of tropical cyclone formation are currently quiet.

However, some things may be about to start to brew. The South Pacific Convergence zone SPCZ is currently quiet in the Coral Sea and is at the northern extent of its position further east. It mainly runs across Solomon Islands, Tuvalu, Tokelau, Northern Cooks and then to the southeast between Southern Cooks and French Polynesia. There are also some convergence zones over Samoa and Tonga. Some models are picking that a tropical low may form on the SPCZ east of Samoa on Tuesday 17 Jan and move south and peak between Niue and Southern cooks on Fri 20th Jan.

SUBTROPICAL RIDGE STR
The STR is now well formed and mainly along 40S, and looks likely to drift north this week, bringing sunshine to northern NZ. The High in the Tasman Sea today should wander east across central NZ on Tue/Wed/Thu 17/18/19 Jan. There should be some zones of enhanced easterly winds on the northern side of this high.

Another large High is expected to move from Australian Bight across south-end of Tasmania on Sat 21 Jan and into the Tasman Sea on Sun 22 Jan.

TASMAN SEA/NZ AREA
Inbetween those two highs there is a transition time for NZ. One front should cross the South island on Thu 19 Jan; preceded by hot NW winds fresh from Australia and followed by a cool SW wind change. Another front is likely on Sat/Sun/Mon 21/22/23 Jan, followed by a cold southerly – but timing and intensity of this event is still variable.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 8 Jan

2012-01-07T18:08:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 8 January 2012
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina's indicators in the atmosphere are moderating. The Southern Oscillation Index SOI (30day running mean) increased to around 2.3 when Cyclone GRANT was around and has dropped to 1.79 on Sat 7th Jan.

Recently a MJO cycle of enhanced convection was apparent over northern Australia but this as weakened away.

The South pacific Convergence Zone SPCZ is solid in an active line from Solomons to northern Fiji to central Tonga to Southern Cooks. Lows have formed between Tonga and Niue and near Southern Cooks. The low near is likely to remain much the same and slowly travel southeast.

The Low between Tonga and Niue has a moderate chance of deepening into a cyclone over next few days and may go east then get knocked to the west for a while. Watch and avoid.

SUBTROPICAL RIDGE STR
Big Fat high at 40S to well-east of NZ is a blocking high at present, so that features around it are sometimes being deflected counter-clockwise. It may shift south to 25S by Tuesday 10th and should slowly relax off to the east from around Friday 13th.

High in Aussie Bight should cross Tasmania on Sat 14th and move into Tasman Sea and ridge over central NZ during 14/15 Weekend, bringing them some welcome sunshine.

TASMAN SEA/NZ AREA
Because of the blocking high out-east, there are a few more Tasman troughs this week.
The low near Bay of Plenty is expected to be pushed westwards across Auckland tonight and then fade as it goes south across the South Island by Tuesday. After a break, a weak trough should cross the country on Wednesday and then the remains of a Tasman Low on Thursday--- bringing some welcome rain to southern areas. This should be followed by a showery SW change on Friday, and then there is likely to be a sunny high for many areas during the 14/15 weekend.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 1Jan 2012

2011-12-31T22:39:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 1 January 2012
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina is steady and strong in the atmosphere. The Southern Oscillation Index SOI (30day running mean) was 2.26 on 25 Dec and on 31 Dec. It is likely to persist for the next few months, encouraging the South Pacific Convergence Zone SPCZ and subtropical ridge slightly pole-wards.

That MJO of enhanced convection mentioned last week moving across Australia is now weakening away. That means we may be in for a few quiet weeks in the tropics.

TC GRANT has also weakened away – There is a branch of the South pacific Convergence Zone SPCZ over the northern Coral Sea, with a weak extension towards New Caledonia---- a (new) small Tropical Low may form in this zone during the week, hovering west of Vanuatu for a few days and then broadening over New Caledonia on Thu 5 Jan. It may visit Fiji on Fri 6 Jan and then wander south along the dateline early next week.

The main branch of the SPCZ is still stretching from Tuvalu to Tokelau to Northern and Southern Cooks. As mentioned last week it has formed a tropical low, around 1005 near Southern Cooks. This system is not well placed for development and should move south then away to the southeast.

SUBTROPICAL RIDGE STR
High has nosed across Tasmania and into SW Tasman Sea this weekend, and should move across North Island on Tuesday and Wednesday. Next High is expected to cross Tasmania on Friday 6Jan and spread around Southend of South Island on Sun 8 Jan, followed by a Northerly flow.

TASMAN SEA/NZ AREA
A transitional trough made for a wet end to 2011 in NZ, and thundery conditions for the interior North Island for New Year 2012. Some of the cold air left behind aloft from this trough may induce more inland showers for North Island on Monday afternoon.

After Wednesday's brief High, another transitional series of troughs are expected to bother mainly the South island on Thursday-Friday-Saturday 5-6-7 Jan with a few fronts.

Should be OK coming and going from Northland this week

Changing timezones:
Samoa and Tokelau have sacrificed Friday 30 Dec altogether so that they are now on the western side of the date line and can trade with Australia and NZ on the same days of the week. For those of you on the eastern side of the date line these old verses of Robbie Burns famous rhyme may still apply tonight:
We two have paddled in the stream,
from morning sun till dine ;
But seas between us broad have roared
since the days of auld lang syne.
For auld lang syne, my friend,
for auld lang syne,
we'll take a cup of kindness yet,
for the sake of auld lang syne.
And here's a hand my trusty friend
And give us a hand o' thine
And we'll take a right good-will draught,
for the sake of auld lang syne.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 26 Dec 2011

2011-12-25T17:58:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 26 December 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina continues to increase in the atmosphere. The Southern Oscillation Index SOI (30day running mean) was 2.02 on 19 Dec and 2.26 on 25 Dec. It is likely to persist for the next few months, displacing South Pacific Convergence Zone SPCZ and subtropical ridge slightly pole-wards.

TC FINA briefly formed in the Coral Sea, but encountered strong winds aloft and lost its top… the low centre is still hovering mid way between Queensland and New Caledonia and drifting south or southeast… it is expected to wander and fade to west of or over North Island on Thu /Fri 29/30 Dec.

TC GRANT deepened east of Darwin on Christmas Day, and is expected to weaken as it wanders further east and reaches the Coral Sea around Thu 29 Dec and then may deepen again and move towards New Caledonia by Sat 31 Dec/Sun 1 Jan. Avoid.

Cyclone risk is winding up this week… an MJO cycle of enhanced convection is expected to arrive there this week also some equatorial westerly winds have reached the Solomons, so all is set for good cyclone formation especially in the Coral Sea.

The South Pacific Convergence zone, SPCZ, has been active over Coral Zone, New Caledonia, and Fiji to Niue and to the southeast--(where SE winds are converging into northerly winds) to Fiji, and Samoa to Niue. This part of the SPCZ may drift north and east across Southern Cooks and allow some tropical lows to develop there on Thu/Fri 29/30 Dec. Avoid.

There is a low that has come form the tropics near 34S 160W today and this should over to the southeast and fade by Wednesday.
Another branch of SPCZ has been lurking between Tahiti and Marquesas over past few days, but I think this will fade away soon.

SUBTROPICAL RIDGE STR
Big fat high stalled over New Zealand during the past week and should now wander to east along 40S reaching 150W by Sun 1 Jan. There is a squash zone of enhanced easterly wind between it and the SPCZ.

Next high is likely to nose across Tasmania on Thu 29 Dec and into South Tasman Sea from Friday 30 Dec, brining clearing weather.

TASMAN SEA/NZ AREA
A transitional trough is expected to take from Wed 28 Dec to maybe as long as wed 4 Jan to cross NZ. During Wednesday and Thursday an increasing NE flow is likely to spread a rain band southwards over the North islands. At about the same time a southerly change is expected over the South Island. These may converge together and stall the rain band for a while over central NZ or the northern parts of the South Island. Location, timing and intensity of peak rain are still changing.

As for Northland—winds should become light and variable there for a time on Sun 1 Jan, then another period of easterly winds may occur next week.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM 19 Dec 2011

2011-12-19T02:00:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 19 December 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina is increasing in the atmosphere. The Southern Oscillation Index SOI (30day running mean) was 1.32 on 3 Dec and 2.02 on 19 Dec. It is likely to continue through our cyclone season, displacing South Pacific Convergence Zone SPCZ and subtropical ridge slightly pole-wards.

TC Washi, in the Philippines, turned out to be more severe than its satellite imagery was indicating, and death toll in the landslides is now exceeding 650. As for last Wednesday/Thursday's rain in Nelson, MetService had issued warnings of 500mm+ for the hills from a stalled trough, and this amount was delivered to a wide region also producing landslides.

In the equatorial regions things are changing …. Equatorial westerlies have arrived in Timor Sea and Norherlies have appeared over Coral Sea, just as a MJO cyclone of increased tropical convection arrives in the Coral Sea. Already small tropical lows are appearing—tonight one is near 5S 155E.

GFS and EC models are both now picking formation of a tropical depression near 10S 130E on Tue 20 Dec, deepening into a more intense feature as it makes land fall near Darwin around Christmas Day --- this can still change so please check BOM for updates.

The South Pacific Convergence zone, SPCZ, is active from Coral Zone (where SE winds are converging into northerly winds) to Fiji, and Samoa to Niue. A tropical depression should develop to west of New Caledonia on Tues 20 Dec, deepen and be slow-moving for the Christmas weekend then move SE across /near New Caledonia and weaken away by 29 Dec. Worth avoiding.

A sub-tropical low is expected to form between Minerva and Niue on Fri 23 Dec, move SE deepen and peak near 35S 160E on Sun 25 Dec and then move further SE and weaken, leaving behind a tropical trough/convergence zone worth avoiding.

SUBTROPICAL RIDGE STR
Large High at 45S is slow-moving over NZ/180 area this week — there is a squash zone of enhanced easterly winds between this and the SPCZ, mainly near 20 to 30S this week. Next week the main part of this high is likely to get east of NZ, and the squash zone may turn into a strong NE flow onto northern NZ during the spring tides following the New moon. Be aware of this strengthening NE with the approach of New Year.

TASMAN SEA AREA
NE tail winds for start of Sydney-Hobart race on 26th, then, in typical fashion, a deep tropically enforced LOW is expected to cross Tasmania around Thu 29 Dec, followed by a intense cold high--- strong pressure gradient between high and low makes for a southerly buster around Friday 30 Dec … maybe too late to bother the race this year, maybe not - Depends on the timing.

Next Sunday is Christmas Day. I'll take time-out to feel the spirit. So, next edition of weathergram will be Monday 26 Dec.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 11 Dec 2011

2011-12-10T19:05:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 11 December 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina is increasing in the atmosphere. The Southern Oscillation Index SOI (30day running mean) was 1.32 on 3 Dec and 1.61 on 10 Dec. This La Nina is likely to continue through our cyclone season, displacing the South Pacific Convergence Zone SPCZ somewhat southwest of its normal position and thus helping promote a quieter-than-normal cyclone season in our area.

There was a MJO – an enhanced pulse of tropical convection – over Western Australia last week but it seems to be fading away before it gets to the Coral Sea, so I now think the cyclone threat in the South Pacific remains low for the next few weeks.

SPCZ weakened and split into two last week, one zone from Solomons to Northern Vanuatu, and other zones near Tokelau, Southern Cooks and Southern French Polynesia, only weakly kinked together. The weather engine in the South Pacific is turning over more slowly than normal. A LOW may form out of the zone near Southern Cooks; its passage to the south may be blocked by a HIGH for a few days but should be able to get going from Thu/Fri 15/16 Dec. leaving behind a zone of rising pressure and light variable winds over Southern Cooks /Niue. OK for diving, no good for sailing.

SUBTROPICAL RIDGE STR
The long wave pattern seems to still be dominating the weather in our part of the South pacific, with a long wave ridge near the date line and a long wave trough to south of Australia.

The surface HIGH that is east of NZ has been acting like a road block to troughs upstream over recent days, and should continue like this until Tue 13 Dec, then weaken and move east along 45S

Next high should push across Tasmania into the South Tasman Sea on Sat 17 Dec. This is expected to take a pat along 50S, crossing southern NZ around Mon 19 Dec and then blossom when it encounters upper support from then long wave ridge and expand to 1030+ to Southeast of South Island on Tue 20 Dec.

TASMAN SEA/NZ AREA
NZ may be next to a long wave ridge, but will spend the next week under attack from some short wave transitory troughs.
The first produced a small area of intense rain between Norfolk and Raoul yesterday, and its low is fading as it moves south along 160E tonight. Remaining rain band is visiting northern NZ next few days: may be useful over Northland Sunday night / Monday and briefly heavy over Taranaki/Nelson high ground on Monday.

This trough may act as the entree and help condition NZ's atmosphere to enhance the impact of the main course: a new LOW should form in the Tasman Sea on Tues 13 Dec and take its time, finally crossing North Island on Sunday 18 – some models have this feature going faster than this. It is preceded by a frontal zone that is expected to cross NZ on Thu 15 Dec and followed by an upper trough good for scattered outbreaks of thunderstorms and finally some cooler south to southwest winds. If a southerly crosses Canterbury on Thursday afternoon it may be preceded by hot air and the cold shock may trigger hail.

For those still planning to sail into Northland:
Northeast winds over Northland this week, these are likely to be strong on Thursday ahead of the front (avoid Thu) then northwest and showery until Sunday. Next west to southwest/southerly winds for Northland are likely on Sun /Mon 18/19 Dec.

I will be travelling next Sunday, so next edition of Weathergrams is postponed to Mon 19 Dec.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 4 Dec 2011

2011-12-03T20:38:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 4 December 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Welcome to the months of the southern summer. For practical purposes many climatologists take the months of December to February to be summer, but for logical reasons I wait until the Solstice for my summer to start.

Either way, the southern hemisphere cyclone season seems set soon to start, with what looks to be a developing tropical depression in the Indian Ocean neat 13S 90E today, possibly set to take a path to the southeast but to fade before making land fall between Shark Bay and Perth in WA around Sun 11 Dec. It is riding on the wave of a zone of enhanced tropical convection, called a Madden Julian Oscillation or MJO that seems set to bring the Monsoon from Indonesia to Northern Australia over the next few weeks.

Australia had a very wet November and is still a place favoring upper troughs, whilst the upper ridge partners have been favuored about and east of the date line.

La Nina is increasing in the atmosphere. The Southern Oscillation Index SOI (30day running mean) was 1.0 on 26th Nov and 1.32 on 3 Dec. It is likely to continue through our cyclone season, displacing the South Pacific Convergence Zone SPCZ somewhat southwest of its normal position and thus helping promote a quieter-than-normal cyclone season is our area. The MJO is likely to reach the Coral Sea around mid-December, so that is likely to be the first period of increased threat.

SPCZ weakened west of the date line last week, from Solomons to northern Vanuatu to north of Fiji, and strengthened east of the dateline from Samoa to Southern Cooks. That little low near 25S 165W today is attached to a branch of the SPCZ which is active over the Southern Cooks. The Low is expected to wander to SE and the activity should ease by wed 7 Dec.

SUBTROPICAL RIDGE STR
Large High at 35 to 40S east of NZ and south of Southern Cooks managed to reach over 1040 hPa last week … It is now slowly weakening and moving east mainly along 30/35S.

New High is expected to cross Tasmania on Mon 5 Dec and then build in the mid Tasman Sea and cross southern and central NZ on Fri 9 to Sat 10 Dec. This has the makings of a fine arrangement for pre-Christmas outdoor functions in NZ next weekend.

TASMAN SEA/NZ AREA
Between the Highs there are troughs. The one over Tasman /NZ today is in two parts… first frontal rain band is over much of the northern areas of both Island tonight and should clear off on Monday. Second part is expected to deepen into a Low in mid-Tasman during Monday and then cross northern and central NZ on Wednesday along with some heavy downpours. After that second rain band moves off, the incoming high is expected to bring dry and clearing weather to NZ, good for a few days of haymaking.

Avoid the Tasman from Mon 5 to Wed 7 Dec.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 27 Nov 2011

2011-11-27T01:01:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 27 November 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

There was a solar eclipse with the New Moon on Friday and this is a Perigean moon. The perigee (= moon-closest-to-earth) occurred 30 hours before new moon. This means that the tides over weekend and on Monday are more extreme than normal - but not quite as extreme as this time last month (Oct perigee was within 7 hours of New moon).

We are having a minor La Nina. From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 18 Nov it was 0.90 and on 26th 1.0. Computer modelling suggests it will continue for next few months, possibly making for a quieter than normal cyclone season. At this stage the first Madden Julian oscillation- a period of enhanced convection –may be starting to appear to west of Australia over next week or two, and so this is an early indication it may reach the South Pacific around mid December.

Last week was reasonably quiet on the South pacific. The South Pacific Convergence Zone SPCZ has two branches: one from Solomons to northeast Vanuatu to Fiji/Wallis/Futuna to Samoa, and the other from Tokelau to Northern Cooks. It is expected to stay is much the same position for the next week or so.

SUBTROPICAL RIDGE STR
High that is crossing to east of northern NZ today should move smartly along 35S over the next few days. Another HIGH is expected to develop at around 40S to 45S in the Tasman Sea on Monday and to spend this week travelling sedately eastwards, crossing the Chatham Islands on Tues/Wed 29/30 Nov. There should be a humid and muggy northerly flow over NZ (and an easterly flow for Northland) for several days.

Another High is expected to travel across Tasmania on Thu /Fri 1 and 2 Dec. This is expected to travel east along 45S, crossing South Island on Wed/Thu/Fri 7/8/9 Dec. More on this in the next weathergram.

TASMAN SEA/NZ AREA
Between the Highs there are troughs. One of these is moving across NZ Sunday night and Monday, and should bring some heavy rain to western South Island and some strong to gale NW winds to southern and eastern districts, but just a moderate wind change to Northland.

Next trough should cross NZ on Sat 3 to Mon 5 Dec, and bring a change in Northland from Sun 4 Dec to West then SW then SE winds.

SAILING TO/FROM NORTHERN NZ.
There are still some cruising yachts sailing to NZ, and indeed this looks to be a good week to approach from the north, with the high now at 35S pulling off to the east at last, so that there is a northerly flow over Northland on Fri/Sat 2/3 Dec. Even the trough crossing Northland may be OK for anyone arriving Sun 4 Nov, but it may deepen into a low on Mon/Tue/Wed 5/6/7 Dec and that may be worth avoiding.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 20 Nov 2011

2011-11-19T22:02:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 20 November 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina continues in a weak to moderate fashion. From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 11 Nov it was 1.02, AND ON 18TH, 0.90 Computer modelling suggests it will continue into the southern hemisphere cyclone season, but as a minor player, making a quieter than normal cyclone season.

The first tropical depression of the new cyclone season made its appearance during the past week, bringing several days of heavy rain to northern Fiji and moving across central Tonga. It has moved off to the southeast and faded away now.

The South Pacific Convergence Zone SPCZ has two branches: one from Solomons to north of Vanuatu to north of Fiji, and the other from Tuvalu to Samoa to Southern Cooks. The SPCZ that is now north of Fiji is likely to move onto Fiji and Tonga this weekend 26/27 Nov.

SUBTROPICAL RIDGE STR
The High that has been lingering in north Tasman Sea for past two weeks is finally on its way east, but slowly and will still be able to form a squash zone between it and the front over the South island on Monday—making gusty conditions for central NZ and wet conditions wit that front. Avoid.

This high then mainly lingers at 30S 180, waiting for a Low to go east of NZ, and finally the High is expected to move off to east itself on Wed/Thu 24/25 Nov.

New High is expected to move across Tasmania on Thu 24 Nov and weaken as it extends across northern NZ on Fri/Sat 25/26 Nov

TASMAN SEA/NZ AREA
On Monday there is an enhanced front + squash zone, a classic spring front, to avoid. A low is expected to form between Christchurch and Chathams on Monday and deepen as it goes east. Another front is expected to cross NZ on Wed 23 Nov, followed by strong SW flow on Thu 24/ Fri 25 Nov (with large ocean swells) and then winds should ease for the election weekend.

SAILING TO/FROM NORTHERN NZ.
If you have Internet access you may be able to check the weather patterns at bit.ly/7daywx or bit.ly/ecoz

For Northland there is, at this stage, expected to be a northerly flow for much of next week, so plan to come south as that high waddles off to the east on Thu 25 Nov and plan to get to Opua before the next SW change (somewhere around 3 Dec).

I plan to be in Nelson for Coastguard conference next weekend… this may delay my next weathergram, depends on how well I travel.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 13 Nov

2011-11-13T02:09:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 13 November 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina continues in a weak to moderate fashion. From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 5 Nov it was 0.88 and on the 11th, 1.02. Computer modelling suggests it will continue into the southern hemisphere cyclone season, but as a minor player. .

The South Pacific Convergence Zone SPCZ extends from northern Coral Sea across Northern Vanuatu towards Wallis Futuna and Tonga. Activity on the SPCZ increased last week and a series of small LOW pressure systems are expected to form near Wallis/Futuna by Mon 14 Nov and then move over Tonga on Tuesday 15 Nov and linger near Niue on Wed /Thu 16/17 Nov. Maybe another may form over Tonga on Friday 18 Nov. Avoid… this area is likely to be full of squally showers all week.

SUBTROPICAL RIDGE STR
High is lingering in north Tasman Sea this week with a ridge occasionally nosing out along mainly 30S--- there is a moderate squash zone of enhanced trade winds in the Tropics between 20 and 25S, lasting all week, especially from Kermadecs/Minerva region to New Caledonia. Be aware of the squash zone and the zone of light variable winds within the STR.

TASMAN SEA/NZ AREA
NZ is continuing with a disturbed westerly flow, typical of spring. Fronts mainly cross the South island on Tue 15 Thursday 17th and Sat 19th Nov, followed by SW flows over the whole country, including Northland, on 16th, late 17th to 18th and on 20th Nov (plus or minus a day). None of these fronts are expected to be major.

SAILING TO/FROM NORTHERN NZ.
If you have Internet access you may be able to check the weather patterns at bit.ly/7daywx or bit.ly/ecoz

Those in Tonga /Niue/Southern Cooks should wait until the SPCZ settles down—maybe early next week. /Fiji/ New Caledonia to NZ is possible, so long as you are prepared for a strong SE for starters, a zone of light winds near 30S, and possible SW winds near Northland (timing of these keeps coming-and-going, so update).

I plan to be in Whangarei on Friday arvo addressing the ICA crowd about weather.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 6 Nov 2011

2011-11-06T01:00:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 6 November 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

La Nina continues in a weak to moderate fashion. From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 30th it was 0.96 and on 5 Nov, 0.88. Computer modelling suggests it will continue into the southern hemisphere cyclone season. This tends to reduce the tropical cyclone activity around and east of the dateline, but may increase the risk around the Coral Sea. But it is a minor player, and other factors are also likely to influence our weather, providing more variety and variability than last year.

The South Pacific Convergence Zone SPCZ extends from northern Coral Sea across Northern Vanuatu towards Wallis Futuna. Also in the past week it has been active across north Tonga /Niue/Southern Cooks and then has stretched southwards into the middle latitudes.
The weak trough that moved to east of Tonga today is expected to continue east and cross Niue on Monday and hover around Southern Cooks from Wed 9 to Friday 11 Nov.
Then SPCZ is expected to move south and build over Fiji/Tonga on the Sat/Sun 12/13 Nov weekend and trigger the development of a LOW to south of Niue that will deepen and move southeast.

SUBTROPICAL RIDGE STR
Last weeks BFH (Big fat High) has moved on. Following that BFH there was a weakness in the STR around NZ, and that helped deflect a low from out of the Southern Ocean so that it could sideswipe southern NZ on Fri 4/Sat 5 with a dusting of snow. Gone now. A new high H1 has formed in the North Tasman Sea… this is a weak one and it should fade into a ridge by Wednesday 9 Nov as another high centre H2 crosses the South Island. H2 should then travel east along 40S to East of NZ. Then another high H3 is expected to form in central Tasman Sea on Fri 11 Nov and move over Northland on the weekend.

So it's a week of rather weak highs and not much in the way of squash zones in the trade winds.

TASMAN SEA/NZ AREA
NZ is getting a disturbed westerly flow inbetween and on the southern side of these weak passing highs. A front is likely to cross the South Island on Tuesday. Another may arrive with 'gusto' over Tasmania on Thursday, and be preceded by a strong NW flow over South Island by Friday morning, then weaken as it crosses South Island on Friday afternoon and fade over the North Island on Saturday. These fronts are not expected to bother Northland much.

SAILING TO/FROM NORTHERN NZ.
If you have Internet access you may be able to check the weather patterns at bit.ly/7daywx or bit.ly/ecoz

Those in Tonga/Fiji/ New Caledonia have reasonable trade winds for departure. There is a disturbed SW flow over Northland until Wed 9 Nov. Then the problem is the way the STR is hovering around Northland, making it a light wind zone, requiring some motor sailing. At this stage it seems that the next front to bring wind to Northland may be a NW on Tue 15 then a SW/S on Wed 16/ Thu 17 Nov.
Note that I will be UNAVAILABLE from 8 to 12 Nov—attending to MetService display at Christchurch show.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 30 Oct 2011

2011-10-30T00:29:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 30 October 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

This new La Nina episode continues in a weak to moderate fashion. From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 22nd Oct it was 1.0, and on 30th it was 0.96. Computer modelling suggests this La Nina will continue into the southern hemisphere cyclone season. This tends to reduce the tropical cyclone activity around and east of the dateline, but may increase the risk around the Coral Sea.

Some Insurance policies take the start of the cyclone season to be 1 Nov- and indeed the risk rises rapidly during Nov and December.

The South Pacific Convergence Zone SPCZ extends from northern Coral Sea across Northern Vanuatu to Wallis Futuna and to Samoa, then … slightly weaker … to Southern Cooks. This is its 'normal position' and it has shown a build up of activity during the last week.

It appears that a tropical Low is forming on the SPCZ around the Wallis/Futuna area during Monday and may move across northern/central Tonga on Tuesday, and then take a path ESE-wards to north of Niue on Wednesday and over Southern Cooks on Thursday, then southwards into the mid-latitudes. Avoid.

SUBTROPICAL RIDGE STR
A BFH (big fat high, central pressure over 1036 hPa) has built well to east of NZ and is hovering around 45S 140W. There is a squash zone of enhanced trade winds on the north side of this high near 25S 150W also enhancing this squash Zone a sit moves slowly south. Avoid.

The next high is expected to form slowly in the mid Tasman Sea around 30S but its formation is expected to be delayed until Sun 6 Nov, and this high may just stay put all next week. During this time there will be the characteristic subtropical ridge link connecting this high to the BFH. The STR link should move north next week to 30S, fading out the squash zone.

TASMAN SEA/NZ AREA
An upper low is forming tonight near 28S 175E and it contains thundery squalls. This feature is expected to be collected by the remains of an old frontal system that is currently draped over southern NZ and a trough that is in the Tasman Sea . The combination is expected to move across NZ on wed 2 Nov and lead in a disturbed W to SW flow that looks likely to cover NZ and the area north of NZ from Thu 3 Nov until at least Fri 11 Nov. Drat.

SAILING TO/FROM NORTHERN NZ.
If you have Internet access you may be able to check the weather patterns at http://bit.ly/7daywx or http://bit.ly/ecoz
Those in Tonga may as well wait for that tropical Low to go away on Tuesday before thinking of departure, just it case it changes track.
The STR will remain as a zone of light winds roughly along 30S from wed 3 Nov until at least Fri 11 Nov, with a disturbed westerly flow over Northland. This isn't the easiest pattern for getting to NZ but we may be able to sort out some zig-zags across the S/SW winds for a few boats with have enough fuel to motor across the STR light-wind-zone.

Note that I will be UNAVAILABLE from 8 to 12 Nov—attending to MetService display at Christchurch show.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 23 Oct 2011

2011-10-22T23:07:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 23 October 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

A La Nina episode is kicking in. From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 16th Oct it was 1.0, and on 22nnd Oct it was 1.2. Computer modelling suggests this La Nina will continue for rest of year and into the southern hemisphere cyclone season.
This helps intensify the subtropical ridges STR and knocks then pole-wards. The stronger highs in the STR helps make stronger trade winds. There is one of these squash zones of enhanced trade winds around New Caledonia and another to NW of Fiji at present, and there is likely to be more of these squash zones this week.

The South Pacific Convergence Zone SPCZ extends from northern Coral Sea across Northern Vanuatu to Wallis Futuna… slightly weak over Tokelau/Samoa the strong again over Northern Cooks. It had a brief welcome visit to Tuvalu mid-last-week, and is expected to drift SOUTH this week.

SUBTROPICAL RIDGE STR
This is a week of Big Fat Highs (BFH)
The one building east of NZ today is expected to make steady progress to the east along around 40 to 45S and grow to over 1030hPa when well south of French Polynesia FP from Wed 26 Oct.

A new BFH is likely to cross Tasmania on Mon 24 Oct and then squeeze around South Island on Wed/Thu 26/27 Oct and then build to maybe over 1035 as moves off to east of NZ from Fri 28 Oct to Mon 31 Oct.

A squash zone of enhanced trade winds is likely to form between this new BFH and the SPCZ=== most likely around 20S to 25S form Tonga to New Caledonia from Friday 28 Oct to Tuesday 1 Nov

TASMAN SEA/NZ AREA
A transitional trough between the two Highs is expected to be windy in the east and west in the west as it crosses South Island on Monday, and then weaken as it stalls over the North Island on Tuesday/Wednesday, 25/26 Oct.

Next trough should reach South Island around Sat 29 Oct --- as a LOW is likely to form off Sydney. This front should stall over central NZ as that Low move SE along the frontal zone. Fronts should then cross Northland around Tue /Wed 1 or 2 Nov, followed by a moderate westerly wind, and Thu 3 Nov followed by a moderate SW wind.

SAILING TO/FROM NORTHERN NZ.
If you have Internet access check the weather patterns at http://bit.ly/7daywx or http://bit.ly/ecoz

The BFHs are in charge this week. One leaves light winds over Northland until Wed 26 Oct then E or NE/NW winds over Northland from Thu 27 Oct to Tue 01 Nov. This provides a good window for arriving in NZ, especially for those leaving Tonga /Fiji/New Cal on Mon/Tue 24/25 Oct. AT this stage the winds over Northland on 2-3 Nov are expected to be mod W /SW, so this may be OK as well.

Because the BFH may be making a squash zone from Tonga to New Cal from Fri 28 Oct to Tue 1 Nov, we may as well treat next weekend as a stay ashore weekend, maybe a good time to complete the voyage planning rather than a target date for departure.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 16 Oct 2011

2011-10-16T01:51:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 16 October 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Northern Hemisphere cyclone season is easing off this week.

A La Nina episode is kicking in. This helps intensify the subtropical ridges STR and knocks then pole-wards. The stronger highs in the STR helps make stronger trade winds. There is one of these squash zones of enhanced trade winds over the seas of French Polynesia at present as a high moves east along 30S and this should last until Tuesday 18 Oct UTC. Another squash zone is expected to form in the Coral Sea on Tuesday 18 Oct UTC and this should spread east reaching New Caledonia /Vanuatu on Thu 20 Oct, Fiji on Fri 21 Oct and Tonga on Sat 22 Oct.

From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 9th it was 0.91, and on 16th Oct it was 1. Computer modelling suggests this La Nina will continue for rest of year and into the southern hemisphere cyclone season. At this stage is expected to be a weak La Nina, and NOT as strong as the extreme La Nina we had last summer.

The South Pacific Convergence Zone SPCZ is expected to hover near its normal position this week between 10 and 15S—this means that Tuvalu and Tokelau may see some desperately needed showers for a change.

SUBTROPICAL RIDGE STR
The week starts with a BFH (big fat high) near 40S 150W moving east – this is the cause of the squash zone over French Polynesia. It is expected to be followed by another High of weaker intensity near 35S 160W from Wednesday 19th October. And another High should form in the Tasman Sea on Tue 18 to Thu 19 Oct, crossing northern NZ on Sat/Sun/Mon 22/23/24 Oct (Labour weekend in NZ)

TASMAN SEA/NZ AREA
Of major concern to anyone sailing to NZ at present is a trough now in the Tasman Sea. One low in this trough is forecast to cross the South Island on Monday and another should cross northern NZ on Wednesday--- this brings vigorous SW winds and heavy SW swells to the zone between northern NZ and as far north as 30S, maybe 25S, on Wed 19 and Thu 20 Oct. AVOID.

For this year's COASTAL CLASSIC departing Auckland for Bay of Islands on Friday,
The forecast at this stage is for a ho-hum SW between 10 and 20 knots.

SAILING TO/FROM NORTHERN NZ.
The main thing is to avoid 25S to NZ on Wed 19 and Thu 20 Oct, please

There is a squash zone slowly spreading east from Coral Sea, expected to reach New Caledonia around Thu 20 Oct and onto Tonga by Sat 22 Oct. It may be a good idea to depart before this zone arrives.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 9 Oct 2011

2011-10-09T03:04:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 9 October 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Cruising sailors in South Pacific may be in for an interesting delight this weekend /next week with the waning moon, especially around the third quarter- This usually triggers a spawning of a coral worm called Palolo (or Balolo in Fijian). Sometimes the overnight spawn may be large enough to colour the sea – stuff can be netted and eaten raw or cooked. Ask the locals.

Northern hemisphere cyclone season is still busy: PHILIPPE still in North Atlantic, staying offshore, and now IRWIN and JOVA in NE Pacific.

Equatorial ocean temperatures in west pacific are near normal, and in east pacific are below normal. A La Nina episode is kicking in. This helps intensify the subtropical ridges STR and knocks them pole-wards (in both hemispheres). The stronger highs in the STR help make stronger trade winds.

From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 2nd Oct its 30day running mean was 1.2, and on 9th it was 0.91. Computer modelling suggests this La Nina will continue for rest of year and into the southern hemisphere cyclone season. At this stage is expected to be a weak La Nina, and NOT as strong as the extreme La Nina we had last summer.

The South Pacific Convergence Zone SPCZ gets knocked south by a La Nina. This was certainly the case early this year, and indeed SPCZ has not been visiting Tokelau or Tuvalu much this year… this explains their drought which is now getting desperate. The SPCZ over past week is now hovering between Solomons and inbetween NE of Vanuatu and SW of Fiji. Rather weak.

SUBTROPICAL RIDGE STR
The STR is usually around 30S at this time of the year, but at present seems to be more near 35/40S. And some BFH (big fat high) specimens are on show this week, getting over 1035hPa near 35S 100W and near 37S 140W. These BFHs are also blocking highs so that troughs get directed around them rather taking a normal journey southeastwards. They also strengthen the easterly winds in the tropics on their northern side - be aware of the prospects of a squash zone of enhanced easterly winds between French Polynesia and Niue from Tue 11 Oct, with huge surf/swell over the Cooks. Avoid.

For Tasman Sea, next high should move in from west on Thu 13 Oct, but will be a slow-mover…should fade over Northland on Sun/Mon 16/17 Oct. The following High is likely to catch up with this and cross the North Island more sedately next week from 18 to 20 Oct. If this turns out to be the case, it may offer a few reasonable voyages from Tropics to NZ / Australia.

TASMAN SEA/NZ AREA
Broad multi-edged trough is expected to cross New Zealand this week. First trough already has a tight and intense low centre moving south along eastern Tasman Sea, and this should cross southern NZ on Monday 10 Oct, preceded by strong NE flow over NZ. Second trough has a low that should move east over southern NZ on Wed and then the trough line should cross remainder of NZ on Thu 13 Oct, followed by cold SW flow that may be thundery.

SAILING TO/FROM NORTHERN NZ.
If you are planning to sail from Tonga/Fiji./Vanuatu/ New Caledonia to NZ, then you may be interested in following the ICA All Points Rally, see http://www.islandcruising.co.nz/ for this voyage.

If you time your voyage to depart Tonga/Fiji/New Caledonia before the squash zone of an incoming high arrives (New Caledonia already sat 15 Oct, and Fiji /Tonga by Tue 18 Oct. Also time it to arrive in NZ after the SW winds following Thursday trough have faded away (around 16 Oct) – then that has the offerings of a reasonable voyage.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM 2 Oct 2011

2011-10-02T03:22:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 2 October 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

This edition comes from Ohope beach… "Is that a dark fin I see before me?"
I shall be discussing weather with local community groups here on Monday.

I hope you managed to avoid the stronger than normal tidal currents of the past week, all due to a Perigean new moon - currents should be quieter this week, allowing for better diving :)

Northern hemisphere cyclone season is still going strong. NALGAE is second destructive typhoon to visit Philippines in a week, and OPHELIA and PHILIPPE are still in North Atlantic, staying offshore.

The tropical ocean temperatures in west pacific are near normal, however there is a slow intensification of a cool anomaly around Galapagos --- so there is a tendency towards a La Nina, but it is more in the east than in the west.

From the atmosphere, the Southern Oscillation Index SOI is positive and increasing: its 30day running mean was 0.75 on 21 Sep and 1.2 on 2nd October. First time is has exceeded 1 since April, so yes there a change occurring in the air. Over next few weeks I shall explain what this may do to the coming South Pacific cyclone season.

The South Pacific Convergence Zone SPCZ has been in its normal zone from Solomons to Fiji then southeast across Tonga and to south of Southern Cooks. The eastern side to this zone is weakening at present as a new zone has formed – rather weak - over Coral Sea. This trough is at present linked via upper jetstreams with a mid-latitude feature and should cross New Caledonia on Monday and Fiji on Tue/wed 4/5 Oct and fade over Tonga on wed/Thu 5/6 Oct. Another tropical trough may form between Southern Cooks and French Polynesia this week, speaking up for the 'proper' SPCZ.

SUBTROPICAL RIDGE STR
The STR seems to be south of its norm position of around 25S. That High around 1030hPa near 35 to 40S to east of NZ should continue to migrate along that latitude this week, out to way southeast of French Polynesia--- with a slight enhancement of the trade winds on its northern side.

The next High is likely to take a path along slightly more southern latitudes---around 45S to 47S—crossing Tasmania on Tue 4 Oct and skirting southern South Island on Thu 6 Oct, then spreading north be cover North Island by Sun 9 Oct.

TASMAN SEA/NZ AREA
The low that is currently in the Tasman Sea is under a slow-moving long wave trough and so is likely to take its time crossing the NZ area this week. Its main centre should move onto central NZ by Tuesday 4 Oct, and then form a secondary 'back' in the Tasman Sea on Wednesday 5 Oct. This complex should finally get to east of the North Island by Sat 8 Oct—mostly being pushed off its perch by the rising pressures of the High, rather than moving via its own pressure falling techniques. Some spats of heavy rain with the low's frontal bands are likely here and there Mon and Tuesday, and the cold southerlies arriving on Tuesday may bring a dash of snow to the Kaikoura ranges.

The slow-moving Low crossing NZ is actually GOOD NEWS, as it provides a reasonably steady westerly flow over seas north of NZ from Tues 4 to Friday 7 Oct. OK there may be a mediocre front and southerly change near 30-35S on Saturday 8 Oct, but then the forecast is for light winds over Northland on Sun 9 Oct and steady northerly flow there on Mon/Tue 10/11 Oct. So if you can arrange to depart New cal/Fiji/Tonga at the right time (considering the incoming trough) then a relatively straight forward voyage is in the offering this week. Not 100% but not bad either.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 25 Sep 2011

2011-09-24T23:58:00.000-07:00

WEATHERGRAM

YOTREPS

Issued 25 September 2011

Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Northern Hemisphere is still at peak cyclone season, with HILARY west of Mexico, OPHELIA and PHILIPPE in Atlantic and NESAT about to cross northern Philippines.

The tropical ocean temperatures in mid pacific continue to be near normal, however there are signs of a growing pool of cooler-than-normal sea near Galapagos---so much that it has exceeded USA's Climate prediction centre CPC's threshold and they have called it a new La Nina. It is sort of neutral with bursts of La Nina at times.

From the atmosphere, the Southern Oscillation Index SOI is positive and increasing: its 30day running mean was 0.44 in 17 Sep and 0.75 on 21 Sep. Some lingering La Nina weather patterns persist in the atmosphere, and the Subtropical ridge STR in the Australia/Tasman Sea area is now being taken south of its normal position.

The South Pacific Convergence Zone SPCZ is persisting from Solomons to Fiji then southeast across Tonga and to south of Southern Cooks. The section across northern Vanuatu/Fiji/Tonga is weak at present but is likely to activate from Thursday 29 Sep to Sunday 2 Oct.

SUBTROPICAL RIDGE STR

The STR seems to be south of its norm position of around 25S. That High near 40S in the South Tasman Sea tonight is expected to travel northeastwards across NZ this week and may be located near 30S 170W by wed 28 Sep and then wander southeast to 38S 130W in early October. Its intensity should stay below 1030hpa so that the trade winds on its northern side are likely to be enhanced a little but stay less than strong.

A large area of heavy SW swell associated with a low from the southern ocean is expected to reach NZ south coast by Wed 28 Sep and then move into the eastern flank of the High in early Oct – so avoid the centre of this high as it will have the combination of light winds and heavy swells – no good even for a power boat.

TASMAN SEA/NZ AREA

There is a developing Low between Sydney and Lord Howe Island tonight feeding off the jetstream aloft and the east Australian current from beneath. It should move east along 30S until wed 28 Sep and then when it gets knocked a little to north of Norfolk Island, but may redevelop near and to east of Kermadecs on Fri/Sat 30 Sep/1 Oct. This low has strong to gale easterly winds on its south side, worth avoiding.

After that high crosses central an northern New Zealand on Tuesday 27 Sep, a North to NW flow is expected over the country for the remainder of the week : down-slope winds may be a problem for eastern coastlines, with temperatures foehning up into the 20s.

Looking further ahead a Low from the southern ocean is likely to reach Southland by Sunday 2 Oct, turning the flow over NZ to a squally westerly, then from Mon 3 to Wed 5 Oct next week, this low may deepen east of NZ, bringing a polar chilled southerly outbreak to NZ eastern coastlines. Avoid.

SAILING TO/FROM NORTHERN NZ.

If you are planning to sail from Tonga/Fiji./Vanuatu/ New Caledonia to NZ, then you may be interested in following the ICA All Points Rally, see http://www.islandcruising.co.nz/ for this voyage.

On Mon 3 Oct to Wed 5 Oct a polar chilled flow hits Northland with W then SW then S winds, so don't plan on departing this week unless you are quick enough to reach Northland by end of Sun 2 Oct – and if you come south from New Caledonia, then also watch the progress of that low wandering along 30S.

The terms used are more fully explained in the METSERVICE Yacht Pack.

More info at http://weathergram.blogspot.com

Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 18 Sep 2011

2011-09-18T04:20:00.000-07:00

WEATHERGRAM

YOTREPS

Issued 18 September 2011

Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

North Atlantic, still boisterous with cyclones ROKE and SONCA – they seem to be staying offshore.

The tropical ocean temperatures in mid-pacific are near normal, however there are signs of a growing pool of cooler-than-normal sea near Galapagos--- so much that it has exceeded USA's Climate prediction centre CPC's threshold and they have called it a new La Nina. Over the entire Pacific, it is sort of neutral with bursts of La Nina at times.

From the atmosphere, the Southern Oscillation Index SOI is hovering slightly above zero: its 30day running mean was 0.49 on 10 Sep and 0.44 in 17 Sep. There has been some lingering La Nina weather patterns in the atmosphere last month, but the sub tropical ridge STR is now near its normal position.

In fact: the South Pacific this week seems to be a continuation of last week- with trade winds in the tropics, disturbed westerly winds to south of 30S and the subtropical ridge STR sitting mainly along 25S—something like the seasonal norm, and this week's disturbed westerlies are looking to be quieter than last week's.

SUBTROPICAL RIDGE STR

A steady STR staying along about 25S. STR in this position should maintain fresh to strong SE winds in the Coral Sea.

One weak high cell should cross the North Tasman Sea on Monday 19 Sep and North Island on Tuesday 20 Sep then weaken away. Another high cell is likely to weaken away in north Tasman Sea on Thursday and Friday 22/23 Sep. Next high should advance across Tasmania on Sat 24 Sep, Tasman Sea on Sun 25 Sep and North Island on Mon 26 Sep. These systems are not penetrating past the dateline at this stage.

TASMAN SEA/NZ AREA

Disturbed westerly flow in Tasman Sea latitudes is a good sign--- it is caused by the warmth of the extra sunlight in the Southern Hemisphere getting further south. The stronger temperature difference between tropics and polar regions is what feeds these westerlies. The equinox is around Friday 23 Sep, so this is THE week of the year when we have the strongest temperature difference.

Last week the disturbances were severe at times… hail in Wellington, a tornado in Auckland and, today, more hail in Auckland and Bay of Plenty. It seems that the coming week should be slightly quieter. The main disturbances should cross NZ on Mon 19 Sep (followed by cold air over southern districts), Thu/Fri 22/23 Sep and Sat/Sun 24/25 Sep (with more cold air in the south).

The timing of these sequences may still change and anyone following the Rugby games in NZ can catch an update on the weather forecasts for the games from

http://www.metservice.com/towns-cities/rugby-world-cup-2011

SAILING TO/FROM NORTHERN NZ.

If you are planning to sail from Tonga/Fiji./Vanuatu/ New Caledonia to NZ, then the next few months is the optimum time. You can join the ICA All Points Rally, see http://www.islandcruising.co.nz/, for this voyage. My suggestion is that you try and meet a front at 30S – that way you will avoid meeting a front upon arrival in Northland. -

I'm just back this evening from a great Boat Show in Auckland.

Great new site-- thanks to organizers, and to Auckland City for helping sorting the parking!

The terms used are as explained in the METSERVICE Yacht Pack.

More info at http://weathergram.blogspot.com

Feedback to home: bobmcd@xtra.co.nz

work: bob.mcdavitt@metservice.com

BOBGRAM issued 11 Sep 2011

2011-09-10T23:22:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 11 September 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Three cyclones (KATIA, MARIA and NATE) in the North Atlantic and some areas of interest to wets of Mexico…so Northern Hemisphere Cyclone season is still raging.

The South Pacific this week offers trade winds in the tropics, disturbed westerly winds to south of 30S and the subtropical ridge STR sitting mainly along 25S. The daily maps look reasonably close to seasonal norm, but just for this week.

The tropical ocean temperatures in mid pacific are near normal, however there are signs of a growing pool of cooler-than-normal sea near Galapagos. This has prompted USA's Climate prediction centre to call this a new La Nina, but Australian and NZ climatologists are happy enough to call it neutral - let's compromise with neutral + bursts of La Nina at times.

From the atmosphere, the Southern Oscillation Index SOI is hovering slightly above zero: its 30day running mean was 0.46 on 2 Sep and .49 on 10 Sep. There have been some lingering La Nina weather patterns in the atmosphere--- the STR was further south than normal earlier this month, but is near its normal latitude this week.

SUBTROPICAL RIDGE STR
No large highs this week in our area, just a weak STR along about 25S. Next high should be moving off Australia and along 30S into northern Tasman Sea from Thu 15 Sep to crossing NZ on 22/23 Sep. This provides a good window for sailing westwards across the north Tasman or eastwards across the mid Tasman Sea.

Rising pressures this week over eastern Australia are helping to enhance strong SE winds in the Coral Sea.

TASMAN SEA/NZ AREA
The Low that crossed southern NZ today in followed by a period of squally SW wind and heavy swells in the Tasman/NZ area until at least Wednesday 14 Sep, and these then spread eastwards of NZ as a disturbed westerly flow. Avoid.

Another trough is likely to deepen in the central Tasman Sea on Friday 16/ Sat 17 Sep and cross North island on Sat 17/ Sun 18 Sep then move off to east of NZ - but this feature is still somewhat uncertain, so if it concerns you then get updates on it .

SAILING TO/FROM NORTHERN NZ.
The Island Cruising Association ICA fleet are starting to think about their All Points Rally from Tonga/Fiji/Vanuatu/New Caledonia to Opua. Well, my idea about the best time to leave from any of these places is so that you encounter a front at 30S – one that is followed by a mediocre ridge. The reasoning is that this voyage takes around a week and fronts in this part of the world have a frequency of at least once a week, sometime more frequent. The disturbed westerlies over Northland this week do not offer much opportunity for this pattern. So let's just enjoy another week of tropical bliss this week, and check in again next Sunday/Monday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

BOBGRAM issued 4 Sep 2011

2011-09-04T00:58:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 4 September 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

We are now moving into the month where daylight increases fastest in the Southern hemisphere ---It breaks out onto the Antarctic circle at around the equinox – that's the Antarctic dawn, so its their coldest time of the year. Since the westerly winds of the roaring 40s get their energy from the temperature difference between the tropics and the polar regions, these winds are normally at their strongest and furthest north at this time of the year--- some call these equinoctial gales—I like to think of them as the gales of the Antarctic dawn.

This year things are not quite normal. The tropical ocean temperatures are near normal so the ENSO is in neutral and not having much impact at this stage. However the Southern Oscillation Index SOI is hovering slightly above zero: its 30day running mean was 0.38 on 28 Aug and 0.46 on 2 Sep. This has been producing some lingering La Nina weather patterns in the atmosphere--- and one which has been happening in the South Pacific has taken the current high of the subtropical ridge south of "normal", weakening the roaring 40s.
HOWEVER, it now looks as though the South West Pacific may be in for a period of roaring 40s weather next week and possibly the following week as well.

4 Cyclones are raging in the Northern hemisphere… In NW Pacific TALAS is weakening over Japan and a new one (currently called TC SIXTEEN) is waiting in the winds. Around USA, Southern Louisiana seems to be coping OK with LEE whilst KATIA awaits offshore (KATIA is the replacement name for the now retired name KATRINA).

In our tropics, the South Pacific Convergence Zone got weak over the past week. There are clusters of convection north of Solomons, just east of Samoa and around Northern cooks but northing organised. The main convection that went from southeast of New Caledonia to southeast of Fiji (where it is tonight) is fed by a jet stream rather than convergence--- and will bring squally rain to southern Tonga until late Monday UTC (avoid). This system should continue heading east southeast and bring variable winds of a trough over Southern Cooks on Tue 6 Sep UTC.

SUBTROPICAL RIDGE STR
The current HIGH making its way eastwards across NZ is somewhat south of the normal STR September position, so kiwis should enjoy its light winds whilst they can. Meanwhile it is likely to produce strong trade winds near 20S all the way from about 160W to 180 until Wed 7Sep. Fiji Met Service have a gale warning is place on this squash zone.

Next high is expected to move east off Australia next week , around Tue 13 Sep , and along 25 to 30S into the North Tasman Sea This is the more normal latitude for the STR in September and more indicative of spring and more encouraging to the roaring 4os pattern.

TASMAN SEA/NZ AREA
Between every two highs there is a trough, and in fact there will be a run of troughs across NZ after the High moves off on Thu 8Sep. Firstly a small low may form between New Caledonia and Northland on Friday 9 Sep and then move southeast brushing past NZ's northeastern areas on Sat 10 Sep. This just marks where a trailing upper trough gets moistened by an upper jet - not expected to bring much.

The next trough should be more substantial and should build into a well-wound up low off Sydney by late Friday 89 Sep, and followed by gale force south to southwest winds in the Tasman Sea for Sat/Sun /Mon 10/11/12 Sep, along with strong wet mild nortehrlies over NZ on Sun 11 Sep. Avoid.

Considering the location of the next high being to north of most of NZ, it seems that roaring 40s or disturbed westerlies are likely over NZ during the week Mon-Fri 12 to 16th Sep--- This may change , so read in again next week.

SAILING TO/FROM NORTHERN NZ.
The passing high makes this an OK week to depart or arrive, but NE winds ahead of approaching trough rules out a good departure from Thu to Fri 8 0r 9 Sep.
The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

2011-08-28T04:33:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 28 August 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI is hovering slightly above zero:
its 30day running mean was 0.47 on 20 August and 0.38 on 28 Aug.

Cyclones in the Northern hemisphere… NANMADOL intensity 85kt already responsible for around 10 fatalities in Philippines, heading for Taiwan on Monday 30 Aug, and likely to make landfall in China. And there is one called TALOS waiting in the wings and likely to make landfall on southern Japan later this week. The remains of IRENE (latest reported intensity 70kt) is moving north along US east coast...its dangerous right front quadrant is forecast to mostly miss New York and hit Boston.

South Pacific Convergence Zone SPCZ split into three during past week, one from Solomons and across Coral Sea to New Caledonia has triggered a small low near Lord Howe Island. Another zone lies along 15S from just N of Fiji to Northern Tonga to Southern Cooks--- this zone is likely to help trigger a Low to deepen near 25/30S 150W on Mon/Tue 29/30 Aug that will then move off to South, weakening the winds over southern French Polynesia for a few days. The third convergence zones lies roughly along 10S mainly about Tuvalu and Tokelau, and west of Marquesas. By the end of this week these are likely to all merge into one zone roughly from Solomons to Southern Cooks.

SUBTROPICAL RIDGE STR
STR had upper support over New Zealand area last week (long wave ridge), but there is likely to be a phase shift towards a long wave trough in this region this week.
The high that starts this week moving off to east of NZ along around 45S should split into weaker zones at 30S and 50S by Tuesday 30 Aug and these should move off to the east at different rates.

Of more intensity, a new high last of over 1030 hPa may move into south of Tasmania on Thu 01 sep and then northeastwards across the Tasman Sea to reach northern North Island by wed 7 Sep.

TASMAN SEA/NZ AREA
Remains of the rain /low pressure system that is today near Lord Howe Island should cross NZ area on Mon/Tues29/30 Aug. This should be followed by a westerly flow of increasing intensity on wed/Thu 31 Aug/01 Sep (wet in west/warm in east), and then a trough and southern change on Friday 02 /Sat 03 Sept. The GFS model currently has a deepening low east of the South Island along with this Fri/Sat southerly, making it something of a polar outbreak--- but EC model at bit.ly/ecoz, simply has it as a transition trough leading in the new high. As the day draws near these models may start to get more pieces of the puzzle and resolve the scenario more closely—if this affects you then keep checking. No point in hyping one idea yet when models still disagree.

SAILING TO/FROM NORTHERN NZ.
Avoid departure /arrival on Mon/Tue and reconsider Friday/Saturday, otherwise things are looking good.
The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM issued 21 Aug 2011

2011-08-21T03:30:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 21 August 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI is in the positive and relaxing this week: its 30day running mean was 0.87 on 12 August and 0.47 on 20 August. .

South Pacific Convergence Zone SPCZ is steady in the zone from Coral Sea to New Caledonia. This zone has been caught by a jetstream and is being wrapped into a small surface low that started off near the east Australia coast a few days ago. This system has a few more days to run, mainly between Lord Howe and Norfolk Island and then should move west towards the Queensland coast and fade. Avoid.

There is another convergence zone – strong to east of northern Vanuatu then weak and lying across Wallis and Futuna then southeast towards French Polynesia. This system is expected to remain slow-moving this week, and then is likely to activate early next week with a LOW forming between Southern Cooks and French Polynesia.

SUBTROPICAL RIDGE STR
STR had a few weak weeks in the South pacific and is about to go through a counter-balancing strong period. The BFH Big fat High in Tasman Sea is a slow-mover and should finally reach Northland on Sat/Sun 27/28 Aug and then next week move along 40S to east of NZ. There are enhanced trade winds in a squash zone in the tropics on north side of this high.

TASMAN SEA/NZ AREA
Westerly winds are expected to return to South island by Wed 24 Aug, warming up places east of the divide. A strong gusty NW flow should arrive over much of NZ during the Sat/Sun 27/28 weekend, and an active trough then may cross NZ on Mon/Tue 29/30 Aug.

SAILING TO/FROM NORTHERN NZ.
The squash zone in the tropics is only recommended for spirited sailors and is expected to start easing by end of the week. It is OK until Friday to depart from Northland to north or east, and Sat/Sun 27/28 Aug are looking good as target arrival dates for voyages to Northland.

Congratulations to Bruce Arms for wiping almost 3 days off the record for a solo circumnavigation of Australia. Way to go , bro!.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM issued 14 Aug 2011

2011-08-14T01:25:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 14 August 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI continues to hover in the positive: its 30day running mean was 0.79 on 5 August and 0.87 on 12 August.

South Pacific Convergence Zone SPCZ is steady in the zone from Solomons to Fiji. There is another convergence zone lying from west to east from Tokelau to Northern Cooks sort of along 10S.
That portion of the SPCZ which is over Fiji at present is expected to travel east (the upper winds are westerly), and reach Tonga on Wed 17 Aug UTC and Southern Cooks on Fri 19 Aug UTC and then fade over southern French Polynesia FP this weekend.
The portion of SPCZ near Solomons remains in place and should be able to spread south into Coral Sea by Sat 20 Aug and onto Vanuatu/New Caledonia this weekend.
Maybe some strong SE winds in the western Coral Sea this week.

SUBTROPICAL RIDGE STR
STR is weak over Southwest Pacific at present….a fading high south of FP extends a weak ridge westwards mainly along 25S to south of New Caledonia and then southwards across the Tasman Sea to a high over 1032hPa in the south Tasman sea
--- this Tasman High is centred near 50S at present, shovelling a cold southerly flow onto NZ. It should just slowly wander along 50S to be south of NZ by Thu 18 Aug and then move NE along eastern NZ this weekend and set off to east of North Island along 40S early next week, intensifying to 1038 for a while on Monday 22 August.

TASMAN SEA/NZ AREA
There is a polar blast over NZ today, shepherded by large areas of low pressure to east of the country and that 1032+ high in the south Tasman High. There may be a small low caught in these southerlies and sideswiping the east North Island Coast on Tuesday 16 August UTC intensifying the winds. The polar blast is making for large seas that may peak on Tuesday 16 Aug at around 5m in the eastern Tasman and around 9m between Canterbury and Wairarapa coasts. Avoid.

Southerly winds should turn SE then E and ease, first in the south Wednesday 17 Aug, reaching North Island by Sat 20 Aug.

A new LOW is expected to move across Australia and deepen off its east coast near Sydney on Thu/Fri 18/19 August and then wander to the NE near Lord Howe on Sun 21 Aug and Norfolk around Tue 23 Aug, preceded by an area of strong NE winds. Avoid.

SAILING TO/FROM NORTHERN NZ.
Polar blast winds and sea should ease enough for OK sailing from Northland on Thursday/Friday…after that the NE winds of the next Low may interfere.

It isn't really the right weather for coming south but if you intend to, then Friday/Saturday are looking OK weather for arrival days.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM issued 7 Aug 2011

2011-08-07T00:07:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 7 August 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI continues to hover in the positive: its 30day running mean was 0.76 on 29th July and 0.79 on 5 August.

Galapagos to Marquesas: If you are still looking at this voyage, it seems that there is a slight advantage with the wind to first head off to 3dge 30min S at 100W and then to 6S at 133W and then to Marquesas. Some showery activity is occurring on-and-off around Marquesas.

South Pacific Convergence Zone SPCZ spent most of last week from Papua New Guinea PNG to Fiji/Tonga and has now shifted to be from PNG more to Tuvalu/Samoa/Southern Cooks. That part of the zone which is east of the dateline is likely to wander north and weaken over next few days. The portion west of the dateline will probably stay put.

SUBTROPICAL RIDGE STR
At present there is a dominant and extended example of the Subtropical Ridge STR along 30S from just north of NZ all to way to south of Southern Cooks.

In a weird way the 'Roaring 40s' westerly pattern has gone awry in the Australian Bight so that the STR there has been deflected SOUTHWARDS to near 50S. This part of the STR has one high cell within it that is likely to fade south of Tasmania on Fri 12 Aug and then another cell should wander along 50S to 45S in the South Tasman Sea by Monday 15 Aug.

TASMAN SEA/NZ AREA
NZ starts off with a strong disturbed southwest flow, easing away on Monday/Tuesday 8 Aug.

There is a weak tongue of high pressure across the Tasman Sea linking those two branches of the STR together. This weak link is expected to cross Tasman on Monday 8 Aug and NZ of late Tuesday 9 Aug/Wed 10 Aug. It will bring a period of light winds and clear skies good for frosts and fogs.

The LOW that is over South Australia/New South Wales at present is 'out of position' as far as the normal pattern is concerned. It started in the Southern Ocean and got knocked into the normal STR latitudes by some upper winds--- brought a shock of cold air to Melbourne. Anyway, it should cross the Tasman on Mon-Tue 8-10 Aug and then cross NZ on late wed/Thu–Fri 10.11.12 Aug, proceeded by some warmer NE winds.

This paves the way for a polar blast over NZ on Sat 13th/Sun 14th Aug, shepherded by low pressures to east of the country and an incoming High in the South Tasman Sea. Avoid.

SAILING TO/FROM NORTHERN NZ.
SW flow on Monday is still good for going north. NE on late Tue/Wed is good for coming south. Fronts on Thursday/Friday are probably no good for anyone. Strong SW/southerly wind changes Sat /Sun 13/14Aug worth avoiding. It may be good again for going north early next week.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com

BOBGRAM issued 31 July 2011

2011-07-30T23:48:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 31 July 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI continues to slowly rise; its 30day running mean was 0.5 on 16 July and 0.6 on 22 July and 0.76 on 29th July.

Galapagos to Marquesas: If you are still looking at this voyage, it seems that there is a slight advantage with the wind to first head off to 3dge 30min S 100W and then to 6S 133W and then to Marquesas. Some showery activity is occurring on-and-off around Marquesas.

South Pacific Convergence Zone SPCZ is slowly returning after a weak period. The main band is affecting Solomons Vanuatu and Fiji. There are weak convergence zones along 3 to 5S, and near 15S between Samoa and French Polynesia.

Not much change with the SPCZ during the coming week, except for a low budding off to south of Fiji on Mon-Tue 1-2 Aug then moving off to SE then E, possibly re-intensifying near 30S 150W on Sun 7 Aug, with its trough affecting French Polynesia FP on Sun-Mon-Tue 7-8-9 Aug UTC.

Another trough MAY bud off near New Caledonia on Wed-Thu-Fri 10-11-12 Aug— but unsure at this stage, tune in again next week for an update on that.

SUBTROPICAL RIDGE STR
Subtropical ridge is expected to be strong this week, getting support from aloft. The high that is crossing NZ may stall for most of this week in North Tasman Sea. There should be some enhanced trade winds north of this high cell—affecting the Coral Sea on Mon 1 Aug and this affect spreading east to reach the Fiji area from Fri 5 to Tue 9 Aug – this little squash zone should be OK for sailing but not so good on divers, and should continue east onto Samoa, etc., next week.

Next High cell should cross Australian Bight Thu-Sat 4-6 Aug and eastern Australia Sun-Tue 7-9 Aug.

TASMAN SEA/NZ AREA
High hanging around northern and central areas until Thursday should bring frosts and fogs. There should be enough westerly flow over southern areas to just bring showers in the west, but a Roaring 40s trough on Thursday may bring a cold southerly change to all of NZ on Fri-Sat 5,6 August .

SAILING TO/FROM NORTHERN NZ.
Not a good week for sailing southwards.
OK for sailing northwards from Tues to Friday 2-5 Aug --- depending on how next week's trough near New Caledonia develops.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 24 July 2011

2011-07-24T02:21:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 24 July 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI continues to hover slightly above zero; its 30day running mean was 0.5 on 16 July and 0.6 on 22 July.

Galapagos to Marquesas: The sea around Galapagos now seem to be reverting to normal temperatures. If you are still looking at this voyage, it seems that the direct path is as good as any other. Some showery activity is occurring on-and-off around Marquesas.

South Pacific Convergence Zone SPCZ is having a weak period. There is one band that is active over Solomons and then weakens as it extends SE to east of Vanuatu and about or to Southwest of Fiji. There is also a weak convergence zone in the French Polynesia FP region.

Not much change with the SPCZ during the coming week, except that a trough may form on it around or to south of Fiji/ New Caledonia on 31 July.

SUBTROPICAL RIDGE STR
The high that is east of Tasmania tonight 24 July is shoveling a polar chilled southerly flow onto eastern NZ. It is showery stuff but with enough snow and ice to impede traffic. This High is expected to travel NE across Tasman Sea on Mon and then, when it gets to 30S on Tuesday, to extend itself east along 30S from 160E to 150W, intensifying the trade winds in the tropics and the westerly flow on its south side.
The SE trade winds in the tropics are likely to intensify over the whole South Pacific and reach a peak around Wed/Thu 27/28 July due to this rebuilding of the STR.
The STR may be reinforced by another high cell making its way across central Australia and budding off at 30S around Thu /Fri 28/29 July.

This is a typical weather pattern.

Next weekend: as this STR goes east and when air-pressures start to fall between Fiji/ New Caledonia and NZ: a trough is likely to form – GFS has this by 31 July, and EC has it, at this stage, around 1 Aug. For the EC – see http://bit.ly/ecoz .

'Roaring 40s and a deep low' is the expected pattern for Aussie Bight next week —no sign of the next High until end of next week.

TASMAN SEA/NZ AREA
Polar chilled southerlies should turn to be from the SW and weaken on Monday as that high migrates across the Tasman Sea.

A disturbed westerly flow is then likely for Tue 26 to Sat 30 July, with an embedded front on Wed and Friday.

SAILING TO/FROM NORTHERN NZ.
Useful winds on Tuesday to Saturday--- but check again on the possible trough to north of NZ next weekend, and maybe avoid the fronts on Wednesday and Friday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 17 July 2011

2011-07-17T01:31:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 17 July 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI has jumped up a little in past week; its 30day running mean was 0.03 on 8 July and 0.5 on 16 July.

Galapagos to Marquesas: The seas around Galapagos are slightly warmer than normal. Even so, at present there seems to be little extra advantage is straying from the rhumb line/great circle.

South Pacific Convergence Zone SPCZ is active from northern Coral Sea (near Solomons) in bands --- one to Vanuatu, another to Rotuma area then Tonga, and a third to Tuvalu. That's about it at present and there isn't much shifting about either.

SUBTROPICAL RIDGE STR
After a long wave trough over the Tasman Sea / NZ area for the past 2 weeks, a subtropical ridge has finally managed to make into the Tasman Sea this weekend. This High should move east across NZ on Mon/Tues at 40S and then stretch northeastwards and weaken during remainder of the weak, so not much of a squash zone in the trade winds on its northern side.

Next High is starting to form in Australian Bight, and consists of some polar air – so is a frosty one, being modified as it encounters warmer water (brewing unstable showers). Should cross Tasmania on Sun 24 July and then move NE across Tasman Sea so that it passes by to north of Northland around Thu 28 July… a normal winter path, allowing a disturbed westerly flow over Tasman NZ by late next week.

TASMAN SEA/NZ AREA
A return to the pattern we had in June, with a moist mild northerly flow over NZ as a Low forms in the mid Tasman Sea. This Low may be complex and multi-centred, and there may be strong winds near some of its compact centres… especially one near Lord Howe on Tue 19 July. Its main frontal rain band should stall over the North Island on Thursday/Friday 21/22 July and an easterly flow should stay over central NZ as the Low weakens and wanders east across area north of NZ on the weekend 23/24 July. This should set the scene for a southerly blast over all NZ on Mon/Tue 25/26 July between the low (then moving off the SE) and the incoming High.

SAILING TO/FROM NORTHERN NZ.
Departing from Northland – There are challenges. Avoid that incoming front especially on Wednesday/Thursday, 20/21 July. There may be a window on Friday/Saturday 22/23 July, going clockwise around a passing weakening low. Then take care to double-check the strength of the southerly outbreak that is likely on Mon/Tues 25/26 July.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 10 July 2011

2011-07-10T01:59:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 10 July 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI remains in neutral territory: 0.08 on 3
July and 0.03 on 8 July.

Galapagos to Marquesas: The seas around Galapagos are slightly warmer
than normal and the winds there are now southerly 5 to 15knots. So the
optimum route is to head due west across these southerlies to 95W and
then head for a waypoint near 6S 134W.

South Pacific Convergence Zone SPCZ is active from northern Coral Sea
(near Solomons) to Vanuatu and then weakly active to the Fiji Area. The
part near the Solomons is expected to wander southwards into Coral Sea
this week.
There are strong SE winds over northern Queensland - associated with the
SPCZ and the high pressures stuck this week over central Australia.
There is a minor branch of the SPCZ coming and going from Tuvalu to
French Polynesia. This zone extends a trough to the southeast into the
mid-latitudes and a LOW is expected to form within this trough between
30S and 35S near 135W on Monday UTC.

SUBTROPICAL RIDGE STR
The High that is southeast of French Polynesia today, 10 July, has a
zone of enhanced trade winds on its northern side, but is now moving off
to the east and fading away.
There is a very weak Sub-tropical ridge along 25S across the South
pacific this week- typical of mid winter.
The next high is expected to stay over central Australia until Fri 15
July and cross the Tasman Sea on the 16/17 weekend and then hang around
central NZ during next week.

TASMAN SEA/NZ AREA
The disturbed westerly flow which arrived here last week is set to stay
for next few days. Between the 1020 isobar of the subtropical ridge and
the 960 isobar near 50S there are 80hPa and westerly gradient across the
area-so the embedded squall lines continue to be thundery - and snowy in
the SW mountains.
There is a SW storm near Tasmania tonight 10 July, and this should move
onto southern NZ on Wed 13 and remainder of NZ on Thu/Fri. There may
then be that new High in the Tasman Sea and a deepening low near (or
east of) Chatham Islands, with an eggbeater of a S or SW flow inbetween
harassing eastern coasts of NZ.
Heavy SW swell is likely in Tasman Sea until 14 July - avoid.

SAILING TO/FROM NORTHERN NZ.
Departing from Northland - wait a while: westerlies may be strong at
times until Thursday 14 July. Conditions should turn SW on Friday 15
July with barometer rising above 1012, and that may be OK for a
departure... but check again nearer that time as there may be a problem
low developing between Northland and Tonga next week.
The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 3 July 2011

2011-07-02T23:33:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 3 July 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI remains in neutral territory, dropping from 0.29 on 26 June to 0.08 on 3 July.

Galapagos to Marquesas: The seas around Galapagos are slightly warmer than normal and the SSE winds there are slightly less than normal. It is making more sense to get west as soon as possible and seek the better winds west of 95W. So just one way point may be all that's needed now…somewhere near 6S 134W and then head for Marquesas. The current along this route is meant to be mostly west-going, but one yacht has reported an east-going head current near Marquesas.

South Pacific Convergence Zone SPCZ is active from northern Coral Sea (near Solomons) to the Fiji Area and then to the southeast where it merges with jet streams and the mid-latitude troughs. The troughs are forming a chain of lows between Northland and Tonga tonight, with associated gales and heavy rain, and these are expected to move southeast, fading over eastern North Island on Tuesday.

SUBTROPICAL RIDGE STR
The High that moved across NZ this weekend is expected to peel off to the east along 40S, reaching 120E by next sat 9 July with a zone of enhanced trade winds on its northern side as it travels.
The next high is expected to stay over central Australia until 12 July and then cross Tasman Sea maybe 15 to 20 July. SO this is a week of weak STR in the SW Pacific- typical of winter.

TASMAN SEA/NZ AREA
So what we have this week for Tasman Sea/NZ area is a disturbed westerly flow, strong to gale at times. This will set itself up after the Tuesday Low moves off eastern North Island, and may reach a peak over NZ in wind and cold (and mountain snow) on Thu 7 July, and then again on Sat 9 July, and Mon 11 July.
Heavy SW swell is likely in Tasman Sea from 6 to 12 July – avoid.

SAILING TO/FROM NORTHERN NZ.
Departing from Northland – wait until Tuesday for the winds to turn offshore, then brace for those swells.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 26 June 2011

2011-06-26T00:50:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 26 June 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
Southern Oscillation Index SOI is in neutral territory, staying between 0.26 on 19 June and 0.29 on 26 June.

Galapagos to Marquesas: Slight change. The seas around Galapagos are now getting slightly warmer than normal and the SSE winds there are slightly less than normal. It is making more sense to get west as soon as possible and seek the better winds west of 95W. So just one way point may be all that's needed now…somewhere near 6S 132W and then head for Marquesas. There are some tropical showers 3-5S at 130w.

As for the Panama to Galapagos leg: it is looking better than last week, the ITCZ seems to be a little more north in that area, so it is now a route with light winds, and may be some tail winds on Monday.

South Pacific Convergence Zone SPCZ has reactivated and is mainly draped from Solomons, across Vanuatu and Fiji then to the southeast. There are also some convergence zones over Tuvalu and Tokelau and, unusually, between 2 to 5S from 130w to 160W.

This coming week the SPCZ should stay in much the same place in Coral Sea/Vanuatu, but may drift to north of Fiji with part of it drifting from the south onto Tonga by end of week - and linking with a low or trough that may form around the Kermadecs.

SUBTROPICAL RIDGE STR
New High is taking its time over Australia along 35S, and pushing a tongue across northern Tasman Sea along 30S… this is enhancing the trade winds in Coral Sea into a squash Zone. Fiji MetService has issued a gale warning on this area for tonight.

This high is expected to finally get into the Tasman Sea east of Tasmania at 40S by Tuesday 28 June. This will make for a squash zone between it and a Low that is then expected to deepen in the cold air over North Island. There will be strong SW winds /rough seas / heavy swells in this squash zone and these will travel north and east reaching the area between North Island and Fiji/Tonga on wed/Thu June then ease and move off to the east. Anyone travelling this route may wish to consider waiting until after Thursday for this stretch of ocean to settle.

The high may fade away this weekend with its remnants crossing southern or central NZ, bring frosty air. By early July, a new high cell should form east of NZ along 40S. There will still be a squash zone on the high's northern side: this is likely to re-intensify in Coral Sea over the weekend, but may ease further east.

TASMAN SEA/NZ AREA
The secondary low that crossed the North Island this weekend was cold enough to bring 10cm snow to Ruapehu. There's another of these lows likely to deepen over the North Island on Tuesday—strong cold southerlies for Cook Strait / southern North Island (in squash zone between high and low) and another dose of snow for Ruapehu, especially on Wednesday. This is a typical "Old man southerly", but may be notable as it's the first we have had in a long while.

SAILING TO/FROM NORTHERN NZ.

It may be more comfortable to let this week's Low go first.

As for the next low that may form around Kermadecs early in July: well, still too far away to resolve much detail, but it may be easier to go clockwise around (travelling north) than this Thursday's low, and is NOT expected to have as much strong wind/rough sea/heavy swell.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 19 June 2011

2011-06-19T02:35:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 19 June 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
SOI is in neutral territory, in past few weeks its 30day running mean has risen from 0.18 on 5 June to 0.73 on 12 June then fallen back to 0.26 on 19 June.

Monsoon is making reasonably average progress over India. There may be a tropical cyclone forming east of Philippines and this feature is expected to go NW and make landfall on China but, at this stage, it isn't expected to become intense.

Galapagos to Marquesas: More of the same. Avoid the Equatorial current. Dive south to around 5S 100W and then head almost due west to 7S 133W and then head for landfall. There are some tropical showers north of Marquesas from 135 to 145W mainly along 3S, but these will probably not affect the voyage. But if you are attempting the Panama to Galapagos leg, be aware that ITCZ is strong to south of Panama along around 5N.
South Pacific Convergence Zone SPCZ is having a quite time — some disorganised slumps east of the dateline, and a more organised line stretching from south of Solomons across Vanuatu then SE to south of Fiji where it merges with a mid-latitude trough/front which is travelling eastwards. This trough may trigger the development of a low to south of French Polynesia around 30S 125W towards the end of the week, bit otherwise it looks like a week of trade winds in the Southwest Pacific, good for sailing west.

SUBTROPICAL RIDGE STR
There is still a leftover high in high latitudes, south of the low now crossing NZ — this high should travel northeast to 40S 140W by next weekend.

The STR generally seems to have finally shifted to its normal winter position of between 30 and 40S (it is about time, Tuesday is solstice). There are big gaps between its highs, one high is south of French Polynesia FP today and moving off to the east, enhancing easterly winds over FP. The next is making its way across central Australia and should shoot off a bud along 25S on Tuesday/Wednesday then move into central Tasman Sea along 40S next weekend, causing strong trade winds in the Coral Sea.

TASMAN SEA/NZ AREA
Last lot of cold air in the weekend trough is expected to wander east across North Island on Monday.
Then a weak ridge is expected to cross NZ on Tuesday/Wednesday.
Next 'Roaring 40s trough' should move across Tasman Sea on Tuesday and arrive over NZ from Wednesday night- waves of squally showers until a drying but cold southerly arrives next weekend (as high moves into Tasman Sea). This is likely to bring some useful snow at last to NZ ski fields.

SAILING TO/FROM NORTHERN NZ.
Best day to depart this week is Tuesday. And best day to arrive is Wednesday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 12 June 2011

2011-06-12T01:56:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 12 June 2011
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

NOTICE: Those of you who are on my weathergram list will notice a
change: as from next week I will be sending these from
bobmcd@xtra.co.nz, and so some of you (depending on your settings) may
find these weathergrams in your JUNK folder. If so, simple tell your
email program not to junk bobmcd@xtra.co.nz

Also please note that I helping manage MetService display at Fieldays
and will be unavailable to respond to email 14-18 June.

TROPICS
SOI is in neutral territory, in past week its 30day running mean rose a
little from 0.18 on 5 June to 0.73 on 12 June.

Monsoon has arrived in Mumbai; arrival time is a few days later than
normal this year and so far accumulated monsoon rain is 17% above the
Long Period Average. It has developed a double-barreled low, one to
west of India in Arabian Sea is now Cyclone ADRIAN and t'other, to east
of India, sort of fills the entire Bay of Bengal.

Galapagos to Marquesas: More of the same. Avoid the Equatorial current.
Dive south to around 5S 100W and then head almost due west to 7S 133W
and then head for landfall. No organised tropical showers around. But
if you are attempting the Panama to Galapagos leg, be aware that ITCZ is
strong to south of Panama.

South Pacific Convergence Zone was mainly located from Tokelau to
Australs along with an active clump about and east of Tonga/Niue.
It also has a squash zone on its southeastern side at present (Fiji Met
Service gale warning). It is now mainly around the Northern and
Southern Cooks, and may get to French Polynesia FP and may get to Samoa.

The convergence over PNG links across the Coral Sea with a mid-latitude
trough that is quasi-stationary in Northern Tasman Sea and trails
southeastwards well to east of NZ. A weak 'secondary' low is expected
to wander from west to east along this front/trough line mainly along
30S to 35S from Monday to Wednesday. Not enough to stop sailing between
NZ and Fiji/Tonga but needs to be taken into account.

SUBTROPICAL RIDGE
High in Australasian Bight is about to break free from its block and
should get onto Tasmania on Mon 13 June and cross Tasman Sea to reach NZ
on Thu/early Fri 16/17 June, and then expand along 40S to east of NZ,
enhancing the trade winds from FP to Tonga early next week.
Next high from Australia is likely to wander east across New South
Wales, indicating a possible end to the "low index" weather regime we
have been having for a while. Colder SW winds should then be able to
spread further north across NZ.

TASMAN SEA/NZ AREA
Some cold air is sideswiping Southland and Otago tonight and should
reach Chatham Islands on Wednesday and Thursday.

Another Low is likely to form off Queensland coast by Wed 15 June, and
this one should deepen a lot in mid Tasman Sea on Thursday and then move
SSE across Southland on Sat/Sun 18/19 June. Associated front should
cross NZ area on late Friday/early Sat, preceded by a northerly flow,
accompanied by rain and followed by a showery NW flow.

For Fieldays this year, prospects are for a dying SW on Wed/Thu, a foggy
ridge for Friday morning, then a band of rain starting Friday night,
easing Saturday afternoon, then showers.

For those returning to NZ after the NZ-Fiji yacht race, you can use the
N to NW winds of the Friday/Saturday front to some advantage, and, at
this stage, it looks a though Northern NZ should then have light winds
Sun 19 to Wed 22 June so that should ensure a good enough return voyage.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

BOBGRAM7 issued 5 June 2011

2011-06-05T03:15:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 5 June 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
SOI is in neutral territory and continues to hover just above zero. It
dropped to 0.3 on 22 may and has since continued falling, was 0.18 on 5
June.

No cyclones around at present.

South Pacific Convergence Zone SPCZ has weakened into clumps --- main
clump is around Tonga and Samoa (as a trough). This branch is likely to
stretch eastwards this week (the reason for this lies with the upper
winds). There is another weak zone in the North Coral Sea. This zone
should grow more extensive and spread southwards this week. And a
minor clump around Tuvalu to Tokelau. A zone of showers over French
Polynesia links with a mid-latitude trough.

SUBTROPICAL RIDGE
HIGH well above 1030 at 37S and south of Southern Cooks tonight has a
spread out squash zone of near gale easterly winds on its northern side.
This High has reached its peak and so has the squash zone. The high
should wander off to the east next few days, so that the fading squash
zone may visit the Australs on Tue to Thu 7 to 9 June.

Weak ridge starts to grow over NZ on Wed 8 June and this should expand
into a new High moving east along 40S to east of NZ over the rest of the
week.

SO, between Northland and Fiji - for the Auckland to Fiji race fleet -
there is a slack subtropical ridge over the next few days, and this
should firm into useful trade winds once this new high grows east of NZ.

NZ/TASMAN SEA
Weak trough crossing NZ on Tuesday followed by that growing high on
Wednesday (mentioned above).

The main feature in our region this week seems to start off as a Polar
outbreak affecting Tasmanian on Tue 7 June. This is expected to deepen
into an intense low off the New South Wales Coast on Wed 8 June and then
broaden across the Tasman on Thursday and finally cross central NZ when
it is decaying on Sat/Sun 11/12 June. If you have full Internet access,
then check this out at http://bit.ly/7daywx .

Australians need to be aware that 5 metre swells may form on western
side of this low on Tue/wed 7/8 June.

WHEN TO DEPART NZ?
With the predominantly northerly flow east of NZ over next few days, it
is as OK as it gets for departing east to Tahiti.

The light winds with the Wednesday ridge may make a good departure day
for power vessels going north, but not so good for sailing--- anyway the
incoming NW flow ahead of the Tasman Low closes this window from
Thursday 9 to Sat 11 June.

May be an OK day to sail north with the SW flow which is likely to
arrive after that Low, say on Sun 12 /Mon 13 June. BUT there may be a
deepening low in the North Tasman Sea early next week - and this may
reach NZ around Wed 15 May - that is the outlook from today's run of the
ECMWF model at http://bit.ly/ecoz .

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 29 May 2011

2011-05-29T00:42:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 29 May 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
La NINA is now starting weakening rapidly in the atmosphere - the
Southern Oscillation Index 30day running mean dropped from 1.21 on 8May
to 0.3 by 22May and has remained that low ever since. We are now in
neutral territory.

TC SONGDA is now re-curving and weakening, and should soon fade as it
sideswipes eastern parts of Japan. So the Northern Hemisphere cyclone
season has started.
USA's tornado season this year has been extremely intense. I'm unsure as
to the contributing factors, one may be the fading La Nina - 2008 was
the last time we had a La Nina fade around May/June and it too was an
intense and early tornado season (but not as intense as 2011).

Galapagos to Marquesas: More of the same. Avoid the Equatorial current
as it is against you this year. Dive south to around 5S 100W and then
head almost due west to 7S 133W and then head for landfall. There may
be some tropical showers (~120W), nothing organised.

South Pacific Convergence Zone SPCZ spent last week in a more relaxed
and spread out fashion. There was a section that linked in with a
mid-latitude trough and fed cloud from New Caledonia to NZ last
Thursday. The main SPCZ now seems to be from Coral Sea to across Vanuatu
then Southeast-wards to south of Fiji/Tonga, and is feeding off a
jetstream as well as converging surface winds. This zone is expected
to travel even further south this week and merge with a trough/low near
the North Island around Sat 4 June and then, next week, it is likely to
travel back northwards as the attached trough travels eastwards.

There is another convergence zone loosely hovering between Northern
Cooks and main Island groups of French Polynesia and this should stay
put without much change.

SUBTROPICAL RIDGE/ NZ/TASMAN SEA
High in the Tasman Sea is maintaining a SW flow over NZ. Around mid
week this system is expected to team-up with a trough forming in the
north Tasman Sea and then both should move east as a couplet onto NZ by
late week. The High is likely to progress faster than the low: so
that, by Sat 4 June, the High may be over Chatham Islands and Low may be
to west of Northland: there will be a squash zone of enhanced
northeasterly winds inbetween, along with frontal rain, over
northeastern North Island. A challenging start for this year's Auckland
to Fiji Yacht race.

That Low is expected to be collected by an incoming trough by late Sat 4
June and this combined system should move from west to east across NZ on
Sun 5 May, preceded by NW winds, accompanied by rain, and followed by
S/SW winds.
Another trough is likely to cross NE from west to east on Tue 7/Wed 8
June followed by colder southerlies. So, the weather over NZ is looking
to be unsettled for and following Queen's Birthday weekend.

WHEN TO DEPART NZ FOR FIJI/TONGA?
There is a squash zone forming near 33S in Tasman Sea by end of Mon
30May and this is likely to spread to 175E by Tuesday, ending the
current sailable pattern.
This squash zone should peak over Northland/Auckland on Fri 3/Sat 4 May.
Avoid. The SW change on Sun 5 June is too brief for a comfortable
voyage, for it may be followed too quickly by a trough on Tue/Wed 7/8
June. At this stage the next comfortable looking weather pattern may be
around 10 June. However, it is too far away to be sure.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 22 May 2011

2011-05-22T01:31:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 22 May 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
La NINA is now starting weakening rapidly in the atmosphere - the
Southern Oscillation Index 30day running mean was 2.55 on 23 April, 1.21
on 8 may and 0.3 today. This is related to a DROP back to normal
pressures around Tahiti.

Now we are two months after the March 21 Equinox and the meteorological
year is building normally... Pre-monsoonal heat is developing in India,
the jetstream have moved off the Himalayas (it is that magic fortnight
called Everest climbing weather). Cyclones are starting in NW Pacific -
SONGDA should develop storm force winds as it re-curves just off the NE
end of Philippines.
And in the Southern Hemisphere the lows of the southern Ocean are
starting to expand their girth, so that a polar outbreak which hit South
Australia in mid May, gave strong winds to NZ from 16 to 18 May, and
brought huge swells to Fiji's South Coast ~20 May.

So, I suppose the Galapagos to Marquesas sailing season is now opening.
It looks OK to go now. Avoid the Equatorial current as it is against
you this year. Dive south to around 5S 100W and then head almost due
west to 6S 133W and then head for landfall. There may be some tropical
showers (~120W), nothing organised.

South Pacific Convergence Zone SPCZ spent last week in active mode from
Solomons to Vanuatu to southern parts of Fiji and then SE to south of
Niue where it mingled in with a passing mid-latitude front. This zone
is now retreating to the north and weakening.

A low is likely to form near 25S 155W by Monday 23 May and then go south
and deepen - may be used as a clockwise helper for vessels on the
NZ/Tahiti route

A new trough should rekindle SPCZ in southern Coral Sea on Mon 23 May.
This should cross New Caledonia on Wed 25 May and Fiji/Minerva area on
Sat 28 May then reach Southern Cooks around Wed 1 June (These features
travel with the upper westerly winds even if the surface winds with them
are modified trade winds). A new Low is likely to form on this trough
around Sat 28 May near 27S 160W and then deepen as it moves South
trough--- another clockwise helper for the NZ to Tahiti crowd.

SUBTROPICAL RIDGE:
Large High is moving east to east of NZ this week. Mainly along 40S.

Next High is expected to cross New South Wales around Fri 27 may and
reach central NZ around Mon /Tue 30/31 May, also along 40S.

These are mediocre anticyclones with average squash zones of enhanced
easterly winds north of them at around 20S. However, for tonight,
there is a squash zone with gale force SE winds near 25S from 165 to
170W between High and Low.

NZ/TASMAN SEA AREA
Between the Highs there is a transitional front and trough. Its clouds
are already active over Victoria and Tasmania tonight, along with some
preliminary troughs that are in mid Tasman. Front is expected to cross
NZ on Tue/Wed 24/25 May, preceded by a strong northerly flow. This
should be followed by the trough on Thursday 26 May--- might be a low
with this over North Island. And then a cold southerly change over NZ
on Fri 27 May - turning into a SE flow over the North Island for Sat 28
May.

WHEN TO DEPART NZ FOR FIJI/TONGA?
The High is now leaving NZ and there is a northerly flow on its western
flank, then the front and trough. SO, it is best to wait now for the
next trough to go by - maybe catch the southerly change on Friday 27 or
go with the SE flow on Sat 28 May.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 15 May 2011

2011-05-15T03:39:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 15 May 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.
Tonight's edition has been delayed by my attending and giving talks at
local Boat Show past 4 days, then catching up on email this evening..

TROPICS
La NINA is now starting weakening rapidly in the atmosphere -the
Southern Oscillation Index 30day running mean was 2.55 on 23 April, 1.21
last week and 0.49 today. This is related to a DROP from higher than
normal pressures around Tahiti.

South Pacific Convergence Zone SPCZ spent last week in active mode from
Solomons to Vanuatu to a zone between Vanuatu and Fiji, with another
branch from Niue to Southern Cooks area. There is now a convergence
zone over Northern Cooks.

The zone of convergence that has been along 5S between 100 to 140W has
started to fade-Puddle jumpers can now set off from Galapagos to
Marquesas

Low tonight 995hpa near 35S 135w is moving off to the SE.

A small low is likely to form on the SPCZ when it is over southern
Tonga/Niue around Thu 19/Friday 20 May. This low may weaken into a
trough as it wanders off to the SE-it should form a zone of strong winds
and heavy swells near Minerva for Thu/Fri 19/20 May, avoid.

SUBTROPICAL RIDGE:
The Big Fat High that was labelled H1 in last week's (and the week
before) weathergram has finally faded. Another HIGH H2 has been
spending last few days crossing the interior of Australia- this
indicates a radical change of season-Highs before this one found the air
over central Australia too thin and warm, but H2 was preceded by cold
air from the Southern Ocean dropping temperatures to abnormal levels
first in Melbourne and, last week in Sydney. SO H2 has found dense
enough air to take the typical WINTER track across central Australia. It
is expected to cross New South Wales on Tuesday 17 May and then cross
Tasman Sea NZ Area along 37 to 42 S from Wed 18 to Sat 21 May- then off
to the east of NZ next week.

NZ/TASMAN SEA AREA
H1 has been feeding a moist NE flow onto the NZ region since Easter,
energizing the local troughs and producing a frontal graveyard that
spent much of last week neat the dateline.

The collapse of H1 has allowed a REGIME CHANGE over NZ: no more NE
flow, now it's a SW flow. The cold front that crossed NZ on Fri 13/Sat
14 has been followed by an unstable/cold west to southwest outbreak.
This flow is likely to stay in place until it is weakened away on
Wednesday by incoming H2.

WHEN TO DEPART NZ FOR FIJI/TONGA?
Winds around Northland/ Auckland may be around 20 gust 30 knots on
Monday Tuesday
--- but are also likely to be 30 gust 40 knots in passing showers, so
that's one reason to delay until Wednesday.
Also the Tasman Sea is filling up now with large swells, probably
peaking in mid Tasman on Tuesday 17 May at around 8 metres! Heavy
swells are likely as far north as New Caledonia and Fiji from Wed 18 May
to Friday 20 May.

Departing from Northland on Wednesday/Thursday seems to be the best -
avoids the possible squally showers on Monday Tuesday and, if your trip
is into part of the north Tasman Sea, these departure days mostly avoid
the big swells.
Those big swells do not have much impact on a trip to Tonga, but we are
expecting some strong winds and heavy swells around Minerva on Thu/Fri
19/20 May due to a brief trough/low forming near Southern Tonga to Niue.

Departing from Friday 20 May onwards puts you in the easterly winds on
the northern side of H2. These winds may be enhanced into a squash zone
near 20S next week, but at this stage things are looking OK - more about
this next week.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 8 May 2011

2011-05-08T01:38:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 8 May 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
La NINA is now starting to weaken in the atmosphere -the Southern
Oscillation Index 30day running mean was 2.55 on 23 April, 1.94 last
week and 1.21 on 8 May .

South Pacific Convergence Zone SPCZ spent last week in active mode from
Solomons to Fiji (some flash flooding in Fiji). There has also been a
rain band hovering around from Niue to Southern Cooks to Gamblers.
And over past week there has been a convergence zone along 5S from 100
to 140W --- this maybe some twinning of the ITCZ, something which
usually happens around the equinox (that was ~6 weeks ago now) and may
be linked to lingering positive SOI. Should fade soon, and puddle
jumpers from Galapagos to Marquesas should wait a few more weeks.

Low is expected to form near Southern Cooks on Tue/Wed UTC with gales,
and then move off to SE, deepening to 998 near 30S 160W by Thursday UTC,
then move further off to S and SSE and slowly weaken. Avoid.

SUBTROPICAL RIDGE:
Intense blocking HIGH (called H1 last week) has been centred east of NZ
and south of Southern Cooks for past week, with pressures rising to over
1038. Fiji Met have had a marine gale warning covering the enhanced
trade winds on north side of this high for past few days 142W to 173W,
20-25S. High has been well supported aloft and has been blocking a
series of lows over NZ area forming abnormal unstable weather. A tragic
tornado over northern suburbs of Auckland last Tuesday faded within 5km
of my place.

This week, this High is finally expected to weaken and more off.

The next High from the west is now NOT expected to be able to get into
the Tasman Sea until Mon 16 May--- so this is expected to be a week when
the subtropical ridge is weak over the South Pacific, allowing
mid-latitude fronts to reach the tropics, and a burst of 'roaring 40'
westerlies to march across NZ and further east.

NZ/TASMAN SEA AREA
After a Monday of light winds and a Tue /Wed of increasing NE flow,
there is likely to be a front Wed night/ Thursday morning (local time)
Then another interlude of light winds, then another front on Friday 13th
(maybe local daytime), and then a burst of strong and squally westerly
winds on Sat 14 May, the wind turning to be more of a southerly on
Sunday 15 May
- this S/SW change gets to the Tasmanian area by Tuesday 10 May and
marks the end of this series of fronts/troughs as it heralds a high
moving into the Tasman Sea.

WHEN TO DEPART NZ FOR FIJI/TONGA?
Again it is not a good week to depart NZ. Either too little wind
between the fronts, or two much NE wind ahead of the approaching fronts.
What we want to look for is the front that is followed by a SW change
that leads in a new High across the Tasman Sea so we can ride these SW
winds to 30S (once they have settled). At this stage, it looks as if
this MAY be the case on Tue 17 May --- and as an added bonus such a
voyage will have some moon-lit nights. More on this, next week.

Heading east from NZ has been hassled by that intense High for past week
or so, but this hassle is now fading.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 2 May 2011

2011-05-02T04:19:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 2 May 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas 6are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Apologies for a delayed edition this week, was too busy travelling on
Sunday.

TROPICS
La NINA is still active in the atmosphere. The Southern Oscillation
Index 30day running mean weakened last week from 2.55 on 23 April to
1.94 on 2 May

South Pacific Convergence Zone SPCZ spent last week in active mode near
20S across the Coral Sea and New Caledonia and to south of Fiji. A low
L1 developed on this zone last Friday, but too far south to be able to
feed off much warm sea... however it has deepened to around 994hPa over
past few days as it moved into central Tasman Sea - and should now
weaken to 1000 hPa as it crosses the South Island on Wed 4 May.

The band that has been appearing along 5S between 100 and 160W started
to break up in the past week. This suggests that reasonable voyages from
Galapagos to Marquesas may start appearing in the next few weeks.

SUBTROPICAL RIDGE:
AN intense 1032+ HIGH H1 was located at 45S 170W today (2 May) and its
squash zone (helped by a few 1005 hPa lows to the north) crossed North
Island mid-last week bringing enhanced rain to Hawke's Bay Coast and
enhanced foehn winds to western NZ between Hamilton and Westport. 'Twas
damaging stuff.

There has been a squash zone between H1 and L1. Not as bad as last
week's but very gusty easterlies on Sunday over northern NZ, leading in
L1's warm front.

The next High, H2, is stuck in the Australian bight for a while ----

NZ/TASMAN SEA AREA

--- and this is likely to allow the cooling southerly winds that it
shovels northwards into the Tasman Sea on Thu 5 May to trigger the
formation of a new Low L2. The models are inconsistent at this stage
with the path for L2 - most likely it will cross central NZ during
Mother's Day weekend, followed by a change to cooler and somewhat
squally W or SW winds, and making this a week of two lows for NZ.

WHEN TO DEPART NZ FOR FIJI/TONGA?
Around the middle of the week there is a gap of lighter winds between
the two lows-maybe OK for motoring north but not for sailing. From Thu
to Sat, the showery NW flow ahead of L2's trough will probably put off
most cruising sailors. There is likely to be some assistance with a SW
to SE wind change after that trough on late Sunday, but this may be
interrupted by a period of light winds in a weak ridge. SO there
appears to be NO great sailing voyages appearing at this stage.

Heading east from NZ is OK in that NW flow, but may be affected by the
NE wind and swell being generated and left behind by H1.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 24 April

2011-04-24T00:20:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 24 April 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
La NINA is still active in the atmosphere.
The Southern Oscillation Index 30day running mean has been on a roll
upwards : from a low of 1.85 on 25 March to a high of 2.55 on 23 April.

That recent pulse of active convection, known as a MJO period, which
brought unsettled weather to North Australia earlier this month, faded
away upon reaching the Coral Sea last week. This was contrary to our
thinking a week ago, showing that the atmosphere is always capable of
nice surprises.

This suggests then that South Pacific is going through a relatively
settled period for the coming week.

The International Tropical Convergence Zone ITCZ lives near 3 to 5
degrees North across the Pacific, and there are signs of a "mirror" to
this near 5S, especially along 100 to 180W. This tends to happen
around the equinox, but that was a month ago so the mirror zone should
break up over next few weeks and then it should be ok to puddle-jump
travel from Galapagos to Maquesas. No rush :)

South Pacific Convergence Zone SPCZ is near the southern edge of its
realm, across the Coral Sea where it is entwined with trough in the
Tasman Sea. Another branch of SPCZ stretches from Vanuatu across Fiji
and Tonga to Southern Cooks, coming and going.

SUBTROPICAL RIDGE STR:
The STR has been knocked south of normal as well.
One High starts this week near 45S 150W, perfectly placed to develop a
LOW on its left shoulder near 30S 160W - close enough to bring a
westerly flow to Southern Cooks and Australs for a few days. There is
an intense squash zone between Low and High to avoid, and the Low is
expected to go SSE and the High goes east, so that the winds in this
squash zone are likely to start out as being from the east and end up as
being from the north.

Of more interest in the NZ area is another HIGH that starts the week at
43S to east of Tasmania. This HIGH is stuck by troughs trafficking over
NZ and finally should be able to swing around southern NZ on Thu 28
April, and then expand over Chatham Islands area on Fri 29 April and
wander further east next week.

NZ/TASMAN SEA AREA
With low pressures to the north and high pressures to the south, an
easterly flow is expected to linger over northern NZ this week. One
rather shallow low is likely to cross Northland on Monday and the marine
part of Bay of Plenty on Tuesday causing an intense squash zone of
southeast winds over central NZ. This low should fade on Wednesday and
Thursday, but the squash zone is likely to build a heavy swell on
Gisborne/Hawke's Bay Coast by Thursday 28 April. Avoid.
On Thursday and Friday another low should deepen-this time in Tasman Sea
near Lord Howe Island --- this Low should move SSE and may cross
southern NZ around Sun 1 May, but there is some uncertainty at this
stage on this track so please update.

These troughs are expected to bring unsettled weather between Northland
and the tropics this week and much of next week, so it is NOT a good
time to plan a voyage north just yet. Patience will be rewarded in May.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 17 April 2011

2011-04-17T01:20:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 17 April 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
La NINA is still active in the atmosphere. The Southern Oscillation
Index 30day running mean has been on a roller coaster ride: from a low
of 1.85 on 25 March to a high of 2.51 on 9 April, and, by 15 April,
relaxed 2.40.

Recent pulse of active convection, known as a MJO period, has been
lowering the isobars in North Australia and has helped form TC ERROL far
to west northwest of Darwin; this system is expected to stay offshore
and go west.

In our part of the world the South Pacific Convergence Zone has been
stretching from North Australia across the Coral Sea and Vanuatu to
south of Fiji and then off to the southeast. Over the weekend a
Tropical depression has formed about and just south of New Caledonia,
taking with it a lot of the activity that was in the Coral Sea.

Fiji Met has a gale warning on the W /NW winds associated with this
system at present. It is already showing signs of fading as it goes SE
--- some of its upper vorticity is expected to be consumed by the trough
that is now getting east of NZ, and help deepen a large LOW to BELOW 980
near 45S 170W on Mon to wed 18 to 20 April. Avoid.

Not much else happening in tropics this week--- but low pressure in
Coral Sea and high pressure in Tasman Sea are likely to keep fresh trade
winds along 20S from New Caledonia to Queensland.

SUBTROPICAL RIDGE:
New autumnal HIGH is crossing Tasman Sea along 37S on Mon 18 April and
then slowly across North Island from Tuesday to Thursday 19 to 21 April.

Next HIGH is expected to form at 45S in South Tasman Sea on Sun 24 April
and then to swing around South Island on Mon 25 (ANZAC Day) and build
over Chatham Islands on Tue 26.

On the northern side of both these Highs, there are likely to be squash
zones of enhanced easterly winds worth avoiding.

NZ AREA
A cold southerly flow dominates eastern areas tonight and Monday, with a
marine gale + heavy swells. Avoid

For this year's Auckland to Tauranga Yacht race starting Thursday
morning a passing High is likely to give light winds--- as that High
moves off on Good Friday, a northerly breeze may help.

Then the next trough should cross NZ on Sat/Sun 23/24 April as a weak
transition southerly change moving from south to north.

It should be Ok for anyone thinking of sailing north from Northland - to
do so Tue to Fri, so long as they route through the subtropical squash
zones properly. Over Easter and for much of the last week of April, NE
winds speak against a smooth voyage.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 10 April 2011

2011-04-11T22:15:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 10 April 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Now that the equinox has faded away, the next thing to watch in this new
'meteorological' year is the jetstream over Tibet. The subtropical jet
in the northern hemisphere is now near the Himalayas so no one will be
climbing Everest yet- but, by mid May, this jet should get further
north and a brief Everest climbing season should occur before the Asian
monsoon kicks in.

TROPICS
La NINA is making a rebound as isobars lower over North Australia. The
Southern Oscillation Index 30day running mean moved from a low of 1.85
on 25 March to 2.51 on 9 April.

In our part of the world the South Pacific Convergence Zone is taking on
a position towards the south end of its range and is defined in a long
stretch from northern Australia across the Coral Sea and Southern
Vanuatu to south of Fiji and then off to the southeast. There is a
tropical depression within this system - tonight it is east of Tanna and
west of Fiji. This system is expected to go SE and deepen to below
1000hPa by Wed 13 April when it is well off to SE of Raoul Island.
Avoid.

A Madden-Julian-Oscillation MJO has been activating convection over
northern Australia recently and is wandering into the west pacific. It
seems to be having more impact in the Northern hemisphere rather than
the Coral Sea.

SUBTROPICAL RIDGE:
A typical autumnal anticyclone is crossing central New Zealand and
should move off to east from Wed 13 April.
Another High is expected to wander over Tasmania on Fri/Sat 15/16 April
and then cross central NZ on Sun/Mon 17/18.

NZ AREA
Between the highs are troughs and lows. Low should deepen just northeast
of Tasmania on Tue 12 April and then weaken and stretch out into a
trough that is likely to move from SW to NE across NZ on Wed 13 to Fri
15 April, followed by a southerly change.

Anyone planning an early get-away from Northland to the tropics may
takeoff over next few days OK; so long they avoid that low from Tanna.
NE to NW flow and a passing trough make for bad days from Wed 13 to Fri
15 April. The SW to SE flow on Sat/Sun 16/17 April make for a few good
days, but these are likely to be quickly followed by an E/NE flow on 18
April onwards, so may as well wait for next window and forget taking off
this week.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 3 April 2011

2011-04-02T22:51:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 3 April 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

We live in interesting times with the weather patterns in transition. NZ
switch from Daylight (summer) time to Standard time today, and the weeks
after the March equinox seem to mark the beginning of a new
meteorological year to go along with the new financial year.

TROPICS
La NINA is making a rebound as isobars lower over North Australia. The
Southern Oscillation Index 30day running mean moved from 1.95 on 20
March to 1.85 on 25 March and back to 2.05 on 3 April.

The eyewall of TC Bune brought torrential rain and gale winds to Raoul
Island, see http://blog.metservice.com/2011/03/the-eye-of-the-storm/.
Then the system unwound and expanded as it rolled away to the southeast
over open sea.

The Intertropical convergence zone ITCZ is showing signs of doing an
equinoctial twining, due to the overhead sun--- one line along 4 to 5N
as normal and another line along 4 to 10S (not normal) all the way from
dateline to Galapagos. Anyone contemplating "puddle jumping" should
wait until at least May for this pattern to fade.

A Madden-Julian-Oscillation MJO has been activating convection over
northern Australia in the past week and is expected to wander into the
Coral Sea this week. This MJO has triggered a tropical depression about
the coast of NW Australia... and this system is expected to be able to
get back to sea next few days and feed off the warmth to possibly grow
into a Tropical cyclone that may make landfall west of Port Hedland on
Thu/Fri 7-8 April. Avoid.

South Pacific Convergence Zone SPCZ stretches from northern Australia
across Coral Sea, New Caledonia, and then to south of Fiji. A jetstream
extends high cloud to south of SPCZ as far as 25 to 30S. SPCZ
(north-edge) is expected to become activated by this MJO during the
coming week, so watch for tropical depressions to develop in Coral Sea
or about New Caledonia. Avoid the Coral Sea this week.

SUBTROPICAL RIDGE:
Two typical autumnal anticyclones to talk about:
HIGH 1 is 1030 tonight near 48S 170W and should wander east along this
latitude to 155W then be forced to take a more southern track by troughs
near 40S.

HIGH 2 is expected to cross Tasmania as 1030 on Tue 5 April then move
very slowly along 40S across the Tasman Sea, expanding to encompass
central NZ from Sun 10 April to mid-next week.

NZ AREA
Between the highs are troughs and lows. A double-barreled trough is
crossing NZ tonight/ Mon 4 April followed by a low deepening off eastern
North Island on Tue 5 April-this should produce southerlies over NZ that
may be cold and wet enough to bring a dusting of snow to Southern Alps.
The disturbed SW flow that follows all this should last until
Friday/Saturday as HIGH 2 approaches.

So we have a week with both a tropical cyclone and the word snow
mentioned - such is autumn.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 27 March 2011

2011-03-26T22:26:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 27 March 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
La NINA is weakening. The Southern Oscillation Index 30day running mean
moved from 1.95 on 20 March to 1.85 on 25 March.

Hmmmm, developments over the past week in Southwest Pacific came from
the east rather than the west (which was where I was looking). A
rejuvenation of the South Pacific Convergence Zone SPCZ spread westwards
along 15/20S from Tahiti to Fiji, and there it stalled and ganged
together on Thursday to form TC BUNE (in Fijian this is pronounced
MBU-NAY).

BUNE has since then been creeping southwards and feeding well on
tropically warm seas, ending slightly west of 180 (the anti-meridian).

This week the main SPCZ is likely to reform from Solomons to Tuvalu to
Tokelau to Northern Cooks, and it might move slowly south.

There is a lot of convection over northern Australia, and strengthening
trade winds over Queensland... There may be the development of a
tropical depression near NW Australia.

SUBTROPICAL RIDGE:
HIGH 1 is a typical La Nina high - wondering along 43S - on Sunday 27
March it is at 140W and moving off to the east.

HIGH 2 is expected to taking a middle route - crossing the Tasman Sea at
40S on Monday 28 March and then being diverted across South island and
along 45S as it works itself east around BUNE on Tuesday 29 March. An
interesting dance.

HIGH 3 is expected to be slightly further north, crossing Australian
Bight and peaking at 1030 on Wed/Thu 30/31 March, then New South Wales,
northern Tasman Sea/northern North Island on Friday/Sat 1/2 March at
1025 or less.

NZ AREA

A trough crossed NZ over the weekend a, leading in a SW flow fresh from
the southern ocean, along with some heavy swell, easing on Monday as
HIGH 2 approaches.

BUNE is now moving out of the tropics into cooler seas so can not
produce high enough clouds to keep its central ring going, but will take
a few days to unravel. That SW flow is expected to reach BUNE on
Tuesday and this may help expand its area of gales and rain. On Mon and
Tue 28/29 March it will dance with a passing anticyclone-they may waltz
or they may tango, we will not really know until it happens. One
scenario is for this to be a tango, moving the wind and rain close to
eastern North Island on Wed/Thu 30/31 March. There are many other
possible outcomes that keep the wind and rain offshore the mainland, so
if this affects you then get updates.

Easterly Swell from BUNE is likely to start reaching North Island
eastern coasts from Tuesday and peak on Wednesday.

Cold front is expected to reach South Island on Thu 31 March and North
Island on Friday 1 April; the NW flow ahead of this system should kick
remnants of BUNE away. The westerlies of the southern ocean are now
creeping steadily north.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 21 March 2011

2011-03-20T22:45:00.000-07:00

WEATHERGRAM

YOTREPS

Issued 21 March 2011

Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

I didn't get time to issue a regular weathergram yesterday == I was driving back to Auckland after attending Central District Fieldays over the past week. So here it is a day later than normal….

TROPICS

La NINA is still strong, and weakening. The Southern Oscillation Index 30day running mean moved from 2.17 on 11 March to 1.95 on 20 March.

There have been some signs of extra convection off the eastern sea-board if Australia, as we expect when a MJO moves into the Coral Sea --- Sydney had a downpour, for example. However, nothing organised has appeared so far, and current thinking is that nothing is likely to become organised in the Coral Sea over the next week or so — we seem to be in a holding pattern at this stage.

South Pacific Convergence Zone SPCZ is loosely draped from Solomons to Fiji and around Southern Cooks and French Polynesia.

SUBTROPICAL RIDGE:

HIGH 1 is typical of a La Nina summer high – wondering off to east of South Island along 45S and then heading NE to around 30S east of 160W.

HIGH 2 is actually one from the sub-polar regions, today 21 March/Equinox it is at 50 to 55S to south of Tasmania. It should wander to east of South Island on Wed 23 March, (World Meteorological day), preceded by a cold southerly, and then go east along 45S from Thu 24 to Sun 27 March, followed by a broad northerly flow.

HIGH 3 is expected to take a more northern route – crossing New South Wales on Mon 28 March and North Island on 1-2 April. A sign that we are now in the equinoctial time of the year, and the roaring 40s are generally heading north.

There are useful trade winds on the northern side of all these Highs.

NZ Area

A sub-tropical low formed on the western shoulder of HIGH 1 — and tonight / Tuesday is moving SE and sideswiping the NE of North Island. It may deepen to below 1000 when east of southern Hawke’s Bay, bringing them wind and rain after a long dry spell - a good chance, too, for Wairarapa and maybe for Marlborough to have an autumn flush, a last chance for some grass growth.

A large sub polar low is expected to follow HIGH 2, with a minor front crossing NZ over the weekend - preceded by a strong N to NW flow on Friday/Sat 25/26 March and followed by disturbed windy and showery W/SW flow on Sunday 27 to Wed 30 March – something more like winter is on its way.

SO it may be an idea to avoid North Island/ Tasman Sea this week

- Weather pattern here should settle by mid next week.

The terms used are more fully explained in the METSERVICE Yacht Pack.

More info at http://weathergram.blogspot.com

Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 12 March 2011

2011-03-12T21:48:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 13 March 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

This weekend my thoughts and feelings are with those displaced by the
Japan quake and Tsunami. Kia Kaha.

TROPICS
La NINA is still strong, and steady. The Southern Oscillation Index
30day running mean moved from 2.19 on 5 March to 2.17 on 11 March.

There are low pressures and persistent convective rain over much of
northern and northeastern Australia, consistent with a new Madden Julian
Oscillation MJO that is now moving into the Coral Sea. It seems to be
weakening as it moves east, and there have been good trade winds in the
Coral Sea for the past week, but the coming week is likely to see
changes--- weakening winds in Coral Sea and increasing convection.

South Pacific Convergence Zone SPCZ is loosely draped over Coral Sea and
Vanuatu, coming and going over Fiji and Tonga and at present to south of
Southern cooks. Another zone is establishing itself along 10S from
Tuvalu to east of Tokelau--- this branch is likely to act as a twin of
the ITCZ around the weeks of the equinox.

SUBTROPICAL RIDGE:
HIGH1 is above 1030 and at 40S to east of NZ today Sunday 13th and
should go east. On Tue 15 March it is expected to fade at 40S but
another cell is likely to form and take over at 45S- and this cell
should head NE to get to 40S 130E by Sun 20 March. As this system
wanders east we can expect enhanced trade winds on its northern side.

A couple of sub-tropical lows are likely to form on the western shoulder
of this High-one between Norfolk and Raoul Island on Wed 16 March and
another to southeast of Rapa on Fri 18 March- these lows are likely to
be shoved off to the south-southeast.

HIGH2 from then Australian Bight should cross Tasmania on Fri 18-Sat 19
March and The South Island on Sunday 20 /Monday 21 March. There should
be an increasing squash zone of east to northeast winds between HIGH2
and lowering pressures in the Coral Sea. Avoid.

NZ Area
A front is poised to move onto southern NZ on Monday 14 March and should
weaken and stall for a few days over South Island, finally fading out
over central NZ on or around Friday 18 March.

On Sat 19 March, another front from Southern Ocean is expected to bring
a wet and chilly wind change to eastern South Island. By then a broad
trough is likely to have developed in the central and north Tasman Sea
and should sideswipe northern NZ.

On Sun 20 that trough should move off the far north as the South
Island's southerly change moves onto eastern North Island (ahead of
HIGH2).

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 6 March 2011

2011-03-05T22:41:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 6 March 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

People in Christchurch have moved from rescue to recovery mode, remember
them at christchurchearthquakeappeal.govt.nz

TROPICS
La NINA is still strong, and steady. Its 30day running mean moved from
2.14 on 26th Feb to 2.19 on 5 March .

There are falling pressures and persistent convective rain over much of
northern Australia, consistent with a new MJO pulse that is expected to
move into the Coral Sea from late this week. Standby for another period
of active weather in SW Pacific next week and until after the Equinox.

South Pacific Convergence Zone SPCZ as returned to its normal position
and is basically sitting over the Coral sea and Northern Vanuatu, coming
and going over Fiji and Tonga and more consistent over Niue and to south
of Southern cooks.
Some BUT NOT ALL models are picking that a series of tropical
depressions may form on SPCZ especially around Vanuatu, Coral Sea and
Gulf of Carpentaria this week. Keep an eye out but do not get diverted
by model extrapolation just yet.
If you have internet keep an eye on http://bit.ly/ecoz for comparative
purposes.

SUBTROPICAL RIDGE:
We seem to be moving into the magical equinoctials already. With the
sun now close to being directly over the equator, the subtropical ridge
is doing a good job in the South Pacific of mixing cool air northwards
and warm air southwards-what we call more 'meridonal' rather than
'Zonal' patterns. Energy is starting to move from the planetary waves
(1 and 2) into the long waves, especially Wave 4. This does mean more
weather in terms of wind and rain between some of the individual high
cells of the STR.

This week in our area HIGH1 is tonight in the South Tasman Sea east of
Tasmanian. There is a squash zone of enhanced trade winds on the north
side of HIGH1 and south side of SPCZ--and Fiji Met have a gale warning
out on this zone for tonight/Monday. HIGH1 should wander east along
around 42 south and fade east of the south Island by Thu 10 March, and a
sub-cell is likely to cross the North Island on Fri 11 March and then
fade away.

HIGH2 is expected to cross Tasmania around Thu 10 March and then rotate
around south end of South Island by Sat 12 March and then get east of NZ
early next week - the Northerly flow on its "backside" is likely to open
a pathway to NZ for whatever may then be forming in the Coral Sea then.
More on this in the next weathergram.

NZ Area
We have had a trough cross NZ over the past few days-it has been
meridonal enough to bring 'southerly rain' to eastern North Island, the
first in about a month to do this, pleasing pastoral farmers and
displeasing apple-pickers.

A small low centre is expected to form within that trough tonight,
making for a day or so of southerly gale on the Hawke's Bay/Gisborne
Coast-good that the restart from Napier for last leg of Round North
Island Race will take off on Monday after this gale.

For remainder of this week there may be a southeast then easterly flow
over northern NZ (this may strengthen over the 12/13 March weekend) and
a disturbed westerly flow over southern NZ. Inbetween places may have
morning mist areas. A weak trough between HIGH1 and HIGH2 is expected
to fade over the South Island Friday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 27 Feb 2011

2011-02-26T21:22:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 27 February 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

That Christchurch quake was devastating. Kiwi people are all one family
and all suffering shock together this week. NZ Govt has set up a fund
to help recovery at christchurchearthquakeappeal.govt.nz

TROPICS
La NINA is still strong, and has strengthened a little in the past week
with its 30day running mean rising from 1.9 on 19th to 2.14 on 26th.

There are falling pressures and persistent convective rain over much of
northern Australia, and this rain is likely to move inland and
southwards this week.

South Pacific Convergence Zone SPCZ was cleaned out when Tropical
Cyclone ATU was vented from the tropics last week. SPCZ is now slowly
redeveloping in the trough left behind, from Solomons to Vanuatu and
then scattered over Fiji and Tonga. East of this zone the flow is
generally from E or NE, and to the west there are light winds over the
Coral Sea.

SUBTROPICAL RIDGE:
HIGH1 is wandering east along 40S to east of NZ and should reach 140W by
5Sat 5 March... the trough on north side of this High is expected to
deepen into a LOW near 30 to 35S around 150 to 160W from Fri 4 March and
there will be a squash zone between this Low and HIGH1. Avoid.

HIGH2 in the Australian Bight is expected to move east across Tasmania
on Sat 5 March, pushing a cold southerly onto NZ on Sat 5 March. This
means there is a long gap between highs over Taman Sea /NZ area and
maybe enough delay so that a LOW may form off Queensland on Fri 4 March
and reach North Island early next week, preventing HIGH2 from getting to
NZ. This scenario may change (read next weathergram).

NZ Area
Weather maps show a trough-troubled week ahead. Low from Tasman Sea is
expected to cross southern NZ on Tuesday 1 March followed by a brief SW
change on Wed 3 March. A much colder front followed by southerly wind
is expected to cross NZ on late Fri 4 March/Sat 5 March, weakening and
stalling over Northland for the weekend. === Another challenging week
for the Round North Island Race fleet

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 20 Feb 2011

2011-02-19T20:15:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 20 February 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong, but weakening. Average atmospheric SOI over 30
days to 19 Feb Jan is 1.9, steady in the past week after dropping 0.5 in
early Feb.

TROPICS
South Pacific Convergence Zone SPCZ spent last week mainly over a wide
altitude zone between 10 and 20 S from Vanuatu to Tonga, with several
regions of tropical downpour. ATU was named near Vanuatu on Saturday. In
Africa (Ghana), the word ATU is occasionally given to a boy born on a
Saturday, so this is seemingly appropriate -however, in Polynesia, ATU
is the Samoan mythical name for the first man to settle in Fiji. The
system is certainly hugging Vanuatu, looking at today's satellite
imagery, may be doing a loop as it slowly re-curves to the south.
Future track is most likely to be south and then southeast--- kicked
along by upper NW winds already in place at 20 to 25S.

ATU is likely to take with it a lot of the energy/activity that is in
the current SPCZ, so it will slowly rebuild after Wednesday along the
trough area that will stay behind over Fiji to Niue. May be OK for some
Island hopping in this hiatus period, but no steady winds.

TC DIANNE off Western Australia is going south and following the Leeuwin
current. It may clip some coastal areas in the process.

King Tides on Sun 20 to Tue 22 Feb, so give these cyclones a wide berth.

SUBTROPICAL RIDGE:
HIGH1 is wandering northeast from 45S 160W to 40S 140W this week, and
maintains a disturbed NE flow on its "back shoulder"(NW quadrant)
HIGH2 starts this week crossing the Aussie Bight and should cross
Tasmania on Friday and then travel northeast across Tasman Sea on Sat 26
Feb and central NZ on Sun 27 Feb.

NZ Area
Transitional trough between HIGH1 and HIGH2 to approach South Island on
Monday (heavy rain tonight in the SW) and cross NZ on Tuesday followed
by a southerly wind change on Wednesday. A challenge for the SIMRAD
Round North Island Fleet sailing counter clockwise from north end to
Wellington, restarting on Tuesday. This trough is expected to linger
off to east of North Island on Thursday as remains of ATU roll SE along
the trough line--- this may throw swells at North Island east coast and
perhaps some rain, but its main wind and rain are likely to be well off
to east. May sideswipe Chathams on Friday.

One more SW to southerly front on Friday, and then clearing weather on
Saturday as HIGH2 arrives. On Sun 27 Feb, there may be a NW flow over
Southland and an easterly surge over Northland/Auckland (just like Wed
16 Feb).

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 13 Feb 2011

2011-02-12T20:58:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 13 February 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong, but weakening Average atmospheric SOI over 30
days to 10 Feb Jan is 1.9, a drop of 0.5 so far this month.

TROPICS
South Pacific Convergence Zone SPCZ is now reforming after being cleared
out by YASI last week. It is mainly between 10 and 15S over western
Coral Sea, with occasional tendrils to New Caledonia, and in an
unorganized zone over Tuvalu to Niue, occasionally extending to Fiji.

This week is likely to be quiet in South Pacific. A LOW may form around
New Caledonia at some stage and go west, but should fade by Friday.
Another LOW may form over southern Tonga area at some stage and then
wander SW to south-of-Fiji then track to southeast on weekend of 19-20
Feb.

The MJO activity is starting again over western side of Australia. TC
BINGIZA is about to make landfall over Madagascar, and computer models
are staring to identify possible tropical lows over Gulf of Carpentaria
or going south and following the Leeuwin current along west coast of
Australia this week.

SUBTROPICAL RIDGE:
Some mobile high cells... HIGH1 is wandering northeast and starts this
week at 1030 hear 45S 160W , maintaining a steady trade wind flow on its
northern side.
HIGH2 starts this week crossing the Aussie Bight and should hug 45S as
it goes east , crossing South Tasman Sea on Tue 15 Feb and moving off to
east of Chathams on Thu/Fri 17/18 Feb. At this stage it looks like it
will be followed by a multiplicity of troughs and fronts over the South
Tasman Sea/South Island area from 19 to 21 Feb.

NZ Area
Transitional front between HIGH1 and HIGH2 is moving east off the South
island tonight.

There is a low near Kermadecs (as there was this time last week) and it
should fade as it comes south, but may edge a little to wets and bring
clouds and showers to Northeastern NZ between Tues and Thu 15 to 17 Feb

Apart from the above, it looks like a typical "La Nina weather week"
for NZ with higher pressure to the south and an easterly flow over the
north. This easterly may weaken over next weekend for the Auckland to
Mangonui leg of this year's SSANZ SIMRAD Round NI race.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 6 Feb 2011

2011-02-06T02:46:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 6 Feb 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over 30 days to 6 Feb
Jan is \
2.6 (an increase of 0.19 since 22 Jan).

TROPICS
YASI strengthened as it crossed Coral Sea to be Cat 5 when it made
landfall over Queensland-the largest since 1918, devastating. It held
integrity as far as Mt Isa and its moisture caused flash floods over
Melbourne on 5 Feb then dissolved into a trough ahead of which the NW
winds hit 40C in Timaru, NZ, today, Waitangi day. Remarkable.

YASI cleared the Coral sea of its energy, and, according to Australian
academics, has ended this active phase of a Madden Julian Oscillation,
MJO, so that the next phase of cyclones may be with next MJO in March.

However, tropical depressions are still occurring. The one near Raoul
Island should move south and fade away next few days, but may have some
impact in Bay of Plenty/Gisborne around Tues 8 Feb. Avoid.

SUBTROPICAL RIDGE:
Next High is expected to cross Tasmania around 8 Feb and hug 45 S and
cross South Island around 10 Feb, then move off to east of NZ followed
by a NE flow.

NZ Area
The transit of that low from Raoul Island on Tues 8 Feb coincides with a
SW/S change over NZ + some big swells from the Southern Ocean into the
Tasman Sea. Avoid. Next trough should cross Tasmania on Fri 11 Feb and
then southern NZ around 14 Feb.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 30 Jan 2011

2011-01-29T22:27:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 30 January 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over 30 days ending 27
Jan is 1.87 (a drop of 0.54 since 21 Jan). .

TROPICS
WILMA followed its expected track and sideswiped Northland and eastern
Bay of Plenty Friday night/Saturday.

ANTHONY lost its top clouds when it re-curved a few days ago, but has
managed to grow some more and get re-named , it now weakening again and
should make landfall between Townsville and Mackay overnight tonight/
around 1am Monday local time.

Another tropical low, just named YASI, is now deepening as it approaches
northern Vanuatu from the east. It is expected to become a major
system and keep going west, gathering energy over the Coral Sea. At
this stage, it is on track to make landfall between Townsville and
Cairns on Thursday 3 Feb UTC. Avoid.

YASI is likely to end this period that has allowed the formation of a
cluster of cyclones, and gradually allow a return of trade winds to the
South Pacific around 5/6 Feb. The South Pacific Convergence Zone SPCZ
has been broken into pieces over past few weeks and should start
reforming along 10 South next week.

SUBTROPICAL RIDGE: STR/ NZ Area.
High/ridge has shifted to 35S in the North Tasman Sea by a shift
northwards of cold air from the roaring 40s. The front responsible for
this northern shift crossed South Island last Friday in time to capture
WILMA and kick it southeastwards, thus limiting its impact on NZ
(thanks).

This high cell is likely to be held in place by an upper ridge until the
5/6 Feb weekend, when it should migrate to east of North Island.

So, it looks like a week of disturbed westerly flow over NZ, with fronts
weakening over the South Island on Monday, Tuesday/Wednesday and Friday.
These fronts may each bring a period of NW gales to eastern districts
and heavy rain about and west of the South Island divide.

Next high is likely to form in Aussie Bight around Sat 5 Feb and move
into Tasman Sea around Sun 6 Feb (Waitangi Day holiday in NZ), pushing a
substantial cold front as S/SW change over NZ. Avoid this cold front.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 23 Jan 2011

2011-01-22T22:43:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 23 January 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over 30 days ending 22
Jan is 2.41 (a slight drop of .05 since 12 Jan). .

TROPICS
Two new cyclones named today. Fiji Met Service is following WILMA: its
centre is likely to circle clockwise to north of Samoa then some south
near America Samoa on Monday and southwest-wards across Tonga on Monday
and Tuesday. At this stage, it may get near Raoul Island on
Wednesday/Thursday and after that track is uncertain. Avoid.

Brisbane Bureau is following ANTHONY, which has formed in the Coral Sea
east-northeast from Cairns. It is currently heading east and should
feed on the warm seas of central Coral Sea over next few days....growing
and growing. This growth is likely to cause the system to loop near 156E
on late Tuesday/Wednesday and then to wander back to WNW where it may
make landfall on far north Queensland over weekend or early next week.
Uncertain at this stage. Avoid.

Another cyclone may form in the Vanuatu to Fiji area around Sun 30 Jan.

The low that deepened to around 990 hPa as it travelled southeast away
from New Caledonia on Saturday is crossing north half of North Island
tonight, taking a track along a trough that was left behind by former
ZILIA. This coincides with a King Tide around midnight. It has gales
around its centre and has already shunted a zone of heavy rain on ahead.
Avoid.

These weather systems have been FAST and FURIOUS lately.

SUBTROPICAL RIDGE: STR.
High/ridge with light winds settling over North Island late Monday 24
Jan and moving off to east on Thu 27. Next High should cross Tasmania
on Fri 28 Jan and then cross North island Area around Sun 30 Jan to
Tuesday 1 Feb, but may have to wait for WILMA's remnants.

NZ AREA.
Remnants of WILMA may be coming south on Fri/Sat 28/29 Jan as a trough
(transitional between highs) crosses the Tasman Sea/NZ area. Details
uncertain at this stage, so if this may affect your plans then watch for
updates. In any event, there should be a new southerly change sweeping
away this trough on Sun 30 Jan, so outlook for Auckland anniversary day
regatta on Mon 31 Jan at this stage is for a dying SW flow.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 16 Jan 2011

2011-01-15T20:39:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 16 January 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over 30 days ending 12
Jan is 2.48 (an increase of 0.18 in the past week). In a La Nina
episode, isobars are lower than normal over northern Australia and
higher than normal over Tahiti. The NZ area is then "piggy-in-middle"
and generally gets more northerly flow than normal. The 2.48 SOI is a
good measure of the extent of abnormality in the weather over northern
Australia. .

TROPICS
We are entering one of the likely busy times of this cyclone season.

South Pacific Convergence Zone SPCZ lies mainly from central Coral Sea
across Vanuatu to Southern Cooks. It is very broad and active, and
early last week heavy rains deluged over Fiji. On Wednesday, TC VANIA
formed. It peaked on Friday, as anticipated in last week's weathergram,
near eastern New Caledonia.
TC Zelia formed on Friday and appears to be reaching its peak tonight
/Sunday as it approaches south end of New Caledonia. It should weaken
back to a tropical Low on Monday 17 Jan.

A Madden Julian Oscillation MJO or pulse of enhanced convection seems to
be making its way into the northern Coral Sea this week. This increases
the chances of tropical cyclone development. A good sign this is indeed
happening is the arrival of equatorial westerly and NW winds over North
Australia. These winds are expected to spread into the northern Coral
Sea over next few days and reach Solomons to Tuvalu by the end of this
week.

Next tropical system to develop is likely to form in western Coral Sea.
GFS & NOGAPS models at present have this occurring around Thu 20 Jan and
EC model by around Mon 24 Jan. Initial ideas are for this system to
track towards New Caledonian area and maybe another system to form near
Fiji as this happens. Plan around these systems.

SUBTROPICAL RIDGE: STR.
New High is expected to ridge across New South Wales on Mon /Tue 17/18
Jan and as it crosses the South Tasman Sea on Wed 19 Jan should link
with a High that had budded north from the Polar Regions to Campbell
Island. This combined High should move NE to area-that-is-east-of-NZ
from Thu 20 to Thu 27 January and expand slowly maybe peaking at around
1038+ next week at 45S to south of the Cooks-this is consistent with La
Nina. There have been very few interruptions in the enhanced easterly
flow over northern Tasman Sea over past six weeks, and this system may
not last long enough but is providing some half-decent trans-Tasman
voyages for a change.

NZ AREA.
Remnants of VANIA are west of Norfolk Island today and heading south and
expected to move southeast across South Island or central NZ on Tuesday.
This coincides with arrival over Southland of LOW from Tasmania. This
LOW has been made from a lot of moisture that has been bothering
Victoria over past few days AND it is followed by a sub-polar high. SO,
on late Tuesday/ early Wednesday, ingredients are in place for a rapidly
deepening low east of the South Island, just as remnants of ZELIA move
southeast across the North Island. Avoid.

On Thursday, conditions should clear nicely with a dying southerly. On
Friday, for Auckland's Big Day Out, an easterly flow is expected to
settle in over North Island along with a lingering trough.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 9 Jan 2011

2011-01-08T22:51:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 9 January 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric Southern Oscillation Index
SOI over past 30 days is 2.3 (a drop of 0.16 in the past week). Dec SOI
was 2.7, a new Dec record and we have to go as far back as Nov 1973
(3.16) to find a higher SOI. This indicates the extent of abnormality
in recent Australian weather maps. Oceanic Nino Index for Sep-Oct-Nov
is -1.4

TROPICS
South Pacific Convergence Zone SPCZ lies mainly from central Coral Sea
across Vanuatu to Samoa and then SE to east of Niue. This is currently
activating between Vanuatu and Fiji and a Tropical Low has formed near
17S 172E.

This system is expected to go SW and pass by close to south end of
Vanuatu, then south then go SE and peak near 25S 173E around Fri 14 Jan
and then weaken over or near North Island area on Sun 16 mon 17 Jan.
Avoid.

Equatorial westerly winds are still well west, just entering the
western Timor sea this week. They are late. A tropical low system should
form off NW Australia around Friday 14 Jan and move off to the SW.

SUBTROPICAL RIDGE: STR.
High in South Tasman Sea is expected to stay there and fade away
allowing a trough and SW outbreak to cross eastern NZ on Wed 12/ Thu 13
Jan . Then a new High 1032+ should roll in from Australian Bight and go
NE across Tasman Sea on Thu Fri 13-14 Jan , and then move quickly away
eastwards along 37S on Sat 15 Jan.

So we have a mobile high crossing the Tasman Sea - this will be useful
for those seeking to escape from Queensland.

TASMAN SEA/ NZ AREA
By Thu 13 Jan Low from central Australia (full of monsoonal moisture) is
expected to move south across Adelaide area and into Australian Bight.
This Low should then wander east along 50S, affecting Tasmania on Fri 14
and Southland on Sun 16. Avoid.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 2 Jan 2011

2011-01-02T02:11:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 2 Jan 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over 30 days ending 2
Jan is 2.56 (an increase of 0.26 in the past week). Oceanic Nino Index
for Sep-Oct-Nov is -1.4

TROPICS
South Pacific Convergence Zone SPCZ is north of its normal location for
this time of the year, stretching across the Solomons to Samoa to near
Marquesas A Madden Julian Oscillation MJO of extra convection has
stalled over northern Australia, and is slowly making its way into the
Coral sea ... the sub tropical jet is deflected south of its norm and is
mostly taking extra moisture that is currently over north Australia
southeastwards to west of south island and filling the hydro lakes (spot
energy price in NZ has gone from extreme high to extreme low is a few
weeks).

SUBTROPICAL RIDGE: STR.
Two cells of High pressure come and go over eastern NZ this week 2-3 Jan
and 5-6 Jan maintaining a warm northerly flow over the North Island.

TASMAN SEA/ NZ AREA
Low is expected to form in Coral Sea on 3 Jan and go south along 160 E
by 6 Jan and deepen to 990 at 37S. Some other lows may form in Coral Sea
on 7 and 8 Jan . And there is a replacement trough (between highs)
crossing much of South Island of NZ on 4 Jan.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM6 issued 26 Dec 2010

2010-12-25T23:53:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 26 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over past 30 days is
2.3 (an increase of 0.15 in the past week). Oceanic Nino Index for
Sep-Oct-Nov is -1.4

A Madden Julian Oscillation MJO of extra convection is appearing over
the Coral sea ... it has already activated things as shown by the brief
appearance of TC TASHA that got to gale force before making landfall
near Cairns on Christmas Eve and then fragmenting inland over Queensland
on Christmas day. Models are producing differing scenarios for where
the next cyclone may form - and maybe not much is likely to happen this
week, except for a tropical low possibly forming near Northern cooks
around Fri 31 Dec and heading for Southern Cooks around sat 1 Jan UTC.
However the chances of formation of a low in the Coral sea are
increasing and GFS is currently producing something there by 4Jan -
EC is as well, but not so intense.

Subtropical jet is conveying the moisture fields from Queensland to NZ
when it gets a chance - when frontal zones allow this --- as is expected
on Mon/Tues 27/28 Dec. Avoid.

SUBTROPICAL RIDGE: STR.
High crossing Tasman Sea and central NZ on Tue/wed 28/29 dec, and next
one is likely from Fri 31 dec to Mon/Tue 3/4 Jan, followed by a strong
northerly flow

TASMAN SEA/ NZ AREA
Front crossing NZ tonight and Mon/early Tues 27/28 Dec is being assisted
by sub-tropical jet. Avoid.

Next trough, on late wed/thu 29/30 Dec, may have separate parts - one
over southern South Island and t'other over northern North island and
should just be a transitional trough between highs.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 19 Dec 2010

2010-12-18T21:36:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 19 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over past 30 days is
2.05 (a drop of 0.05 in the past week). Oceanic Nino Index for
Sep-Oct-Nov is -1.4

TROPICS
South Pacific Convergence Zone SPCZ is in its normal location for this
time of the year, stretching across the Solomons to east of Vanuatu,
moving north and south over the Fiji/Samoa/Tonga area, then weak between
the Northern and Southern Cooks, and then reasonably active again along
south end of French Polynesia. There is a Madden Julian Oscillation MJO
of extra convection making its way eastwards across northern Australia
but weakening. This should wander into the Coral Sea during the coming
week. However, the accompanying equatorial westerly winds so far have
only reached 130E and computer models suggest that they may not be able
to get east of Papua New Guinea during the coming week. So, therefore,
then, there's a slightly increased risk of cyclone development in the
Coral Sea this week, but computers are not picking developments in this
region.

That low centre off the west coast of Australia has sea surface
temperatures around it that are rated to be below the threshold for TC
development. It should slowly wander west and turn into a trough. Of
more interest is what might happen in the Timor and Arafura Seas as the
MJO passes by. Some models are at this stage producing output showing a
TC around Darwin near Christmas Day (shades of Tracy 1974, I can still
remember), but details are all over the place, and the EC model is not
picking any development --- so if that's near you seek updates.

SUBTROPICAL RIDGE: STR.
High to southeast of Chatham Islands is quasi-stationary and should just
slowly wander north from 45S to 30S by Friday 24 Dec and then fade away.

The next high is expected to be able to get from Australia Bight across
Tasmania around Friday 24 Dec and then cross NZ around Sat 25
Dec/Christmas Day and then move quickly off to the east along 40S on
Boxing Day.

TASMAN SEA/ NZ AREA
There is a long wave trough over the Tasman Sea area helping convey
water-vapour from Indonesia, across Australia, to the NZ area. So this
is likely to be a week with three fronts.

The first went across today Sunday, bringing decent rain to the North
Island. The second is likely to be associated with a tight-centred low
tonight forming off the New South Wales Coast ... wind and rain mainly
for South Island on Tuesday, and then weakening over North Island on
Wednesday and Thursday.
The third front should mark the end of this series and lead in a SW
change (a heralding angel for the Christmas Day high), and should cross
the South Island during the day on Friday 24 Dec/Christmas eve, then the
North island that evening.

A note for those planning to sail from Auckland to Bay of Islands for
the holidays - SW winds for this are likely to be few and far between
during next few months, and this SW may only last for the 25th - light
northerlies returning as soon as Boxing Day afternoon.

SYDNEY-HOBART
Still somewhat uncertain, and depends on whether the Timor and Arafura
Seas can produce a tropical low for Christmas or not. At this stage the
idea is that a trough is likely to wander off the New South Wales Coast
around Boxing day, followed by a period of moderate southerly winds
that back to be from east and then northeast by Tuesday 28 Dec.

Check out moonrise on Tuesday 21st (if sky is clear). It is a full moon
right on the solstice and that does not happen often. It will also be a
total lunar eclipse--- the moon will rise into the earth's shadow and
appear red/brown-coloured, so may be particularly memorable.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued Sun 12 Dec 2010

2010-12-11T21:05:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 12 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated. Oceanic Index

La NINA: Still strong. Average atmospheric SOI over past 30 days is 2.10
(a rise of 0.41 in the past week). Oceanic Nino Index for Sep-Oct-Nov is
-1.4 and steady.

TROPICS
South Pacific Convergence Zone SPCZ returned to normal last week, draped
across the Coral Sea and Vanuatu with build ups over Fiji and Samoa. And
there is scattered activity along 15S to French Polynesia FP.

A aging low centre near 25S 170E (to SE of New Caledonia) has a
circulation that is drawing SPCZ activity southwards across Fiji and
Tonga. This centre is expected to fade as it wanders southwards
towards Norfolk Island, and SPCZ activity should continue to hug 15S
this week.

There is a Madden Julian Oscillation MJO of enhanced convection making
its way across the Timor Sea this week and into the Coral sea between 15
and 20 Dec. This should activate the SPCZ. Normally it increases the
risk of cyclone formation, but this MJO is likely to lack a zone of
equatorial westerlies so may not have much impact in the Coral Sea.

Some models are picking that a zone of weak equatorial westerlies may
trigger a tropical low or two to form off NW Australia. The latest GFS
model is picking one to form in Gulf of Carpentaria between Tuesday 14
and Friday 17 Dec and for this to then move SW then S inland towards
Alice as a wet Monsoon Low. In any event an Australian conveyor belt of
upward motion is being set up in the heat trough from North Australia to
Queensland, sometimes reaching Tasman Sea and then onto New Zealand, and
this NW flow in the upper air is likely to last for the next fortnight.

SUBTROPICAL RIDGE: STR.
The STR was knocked north last week but a weak Polar outbreak (polar
index went negative). Southern lows took the opportunity to expand
northwards and one passed by close to NZ - It is now near 45S 165W and
it seems destined to deepen as it wanders north getting as far north as
40S 150W by Wed 15 Dec then exiting to the southeast. Associated High
is making its way east along 30S. Another high is forming just east of
New Zealand tonight Sun 12 Dec. This should wander along 45S on Mon 13
Dec the slide around south-side of that low, but leave a cell near 30S
so that enhanced trade winds are expected all week from FP to Tonga.

Another High is expected to cross NZ Wed /Thu 15/16 Dec and then blossom
east of NZ and slowly shift north to 35S by Tue 21 Dec.

TASMAN SEA/ NZ AREA
Some more southern lows are likely to get near NZ this week. One is
expected to pass by south of Macquarie Island tonight Sun 12 Dec and an
associated front is expected to swipe by NZ on Monday/Tue 13/14 Dec,
followed by a showery southerly change.

A small low may form in the Australian conveyor belt off Queensland
around Wed 15 dec and bring some welcome rain to northern NZ in a NE
flow around Thursday 16/Friday 17 Dec. This may start a trend.

Then another southern low should pass south of Tasmania around Sat 18
Dec as an accompanying low may form off Sydney, feeding from the
activity in the Australian conveyor belt. These lows may dance around
each other around Sun 19 Dec, whizzing close by Southland and blasting a
strong northerly flow across most of NZ. Avoid. Its frontal band is
then expected to cross NZ on Monday-Tuesday 20-21 Dec.

Keep an eye on that conveyor belt as it is likely to continue producing
Lows in eastern Aussie seaboard to NZ area from 23 to 27 Dec, and this
may have an impact of the Sydney-Hobart.
The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 5 Dec 2010

2010-12-04T22:20:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 5 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA: Average atmospheric SOI over past 30 days is 1.69, up a bit
from 1.5 last week.

TROPICS
South Pacific Convergence Zone SPCZ had a week off in the Coral Sea as
all that activity hat was over Fiji last week went across Tonga/Niue and
to south of Kermadecs. The remainder of this is expected to fade and
wander off to east on Mon/Tue 6/7 Dec.

A burst of convection occurred along the Queensland coast over the past
few days, but this is already fading and should be gone by end on Monday
6 dec.

A new SPCZ is likely to form over north Coral Sea this week and wander
south to be from Vanuatu to Fiji by 11/12 Dec. Enhanced convection
along this SPCZ is likely from 15 to 20 Dec due to an incoming Madden
Julian Oscillation--- more about that in next weathergram.

SUBTROPICAL RIDGE: STR.
High near Northland on Mon 6 Dec should fade away on Tues 7 Dec.
High crossing South Tasman Sea on Tue 7 Dec should expand to NE by Fri
10 Dec and then expand as it wanders east along 35S, making a squash
zone of enhanced trade winds on its northern side.

NZ/Australia AREA
Trough between the highs may bring showers- one of these troughs crosses
NZ on Mon 6/ Tues 7 Dec bringing a southwesterly change.

The next moves off Sydney on Thu 9 Dec, onto Brisbane and Southland on
Fri 10 Dec, central Tasman and central NZ on Sat 11 Dec, and then onto
North Island around Sun 12 Dec. By then there may not be much left in
this front, so it shouldn't put anyone off trying to approach Northland
from the north.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 28 Nov 2010

2010-11-27T20:35:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 28 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA: Southern Oscillation Index SOI over past 30 days has eased
from 1.9 to 1.5 standard deviations. The La Nina shows itself on our
weather maps with subtropical ridge being more south than normal in the
Pacific.

TROPICS
South Pacific Convergence Zone SPCZ has been active across northern
Coral Sea to Fiji and, in a more scattered fashion, from Samoa to French
Polynesia.

Moisture within the SPCZ has converged to produce a double-barrelled low
pressure system between Vanuatu and Fiji. The centre of this depression
has been moving east southeast onto Fiji, and may be named as a tropical
cyclone soon.

It has a squash zone of enhanced easterly winds on its south side that
are now around gale force. Some computers are picking that this system
should soon curve off to the south and maybe do a little loop between 25
and 30S near the 180 anti-meridian between Wed 1 and Sat 4 Dec, and then
fade and go off to the southeast.

Anyone intending to sail towards NZ this week should wait for this
system and its swells to move off first.

There was a burst of wet-season-weather on the Queensland coast around
20-22 Nov. There is some rain inland within the Australian heat trough
today and some of this may reach the Cairns Coast on 3 to 4 Dec.

A new Madden Julian Oscillation of enhanced convection is starting to
show signs of possibly reaching the Coral Sea around 10-20 December.
There is no sign yet of any equatorial westerly winds --- these usually
appear in December and can be associated with cyclone development.

SUBTROPICAL RIDGE: STR.
High over NZ today 28 Nov is expected to fade to east of NZ during
Mon/Tue 29/30 Nov.
New high moving over Tasmania at present should slowly cross South
Tasman Sea and South Island 29 Nov to 1 Dec. Then one centre may stall
in Tasman Sea and fade away Sun 5 Dec, and the other move along 40 South
to east of NZ.

NZ AREA
It's another week of high and dry (with some exceptions).

East to southeast flow is likely for Northland, between the low to north
and high to south, from Tue 30 Nov to Sat 4 Dec.

Brief troughs are likely between those highs--- one should bring a NW
flow to the South Island on Mon 29 Nov and SW on Tues 30 Nov. The next
should bring a southerly change from sat 4 to Mon 6 Dec.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 21 Nov 2010

2010-11-20T23:49:00.001-08:00

WEATHERGRAM
YOTREPS
Issued 21 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence Zone has been active across northern Coral Sea
to the Wallis/Futuna area and then stretching off to the southeast of
Tonga. A small tropical low near Wallis/Futuna tonight should fade on
Monday, broadening the trough over and to south of Tonga.

When the cold Southerly winds that are crossing New Zealand tonight
reach this trough over the Kermadecs on Wed 24 Nov --- this is
expected to promote a rapidly deepening and slowly-south-moving Low from
Thursday 25 to Sat 27 Nov--- making for strong southerlies between NZ
and Tonga from 22 to 26 Nov.

So, those staying in Tonga waiting for a comfortable sail to NZ should
keep waiting - may be a brief window around 27-29Nov, but please
recheck.

There's a new branch of the SPCZ budding off the Queensland Coast.
Since we are in the early part of the Cyclone season and have a strong
La Nina, it is to be expected that the SPCZ will spend much of its time
in the Coral Sea, so we can expect this new branch to activate over the
Coral Sea this week, lowering the pressure there. And since there's a
High stalled in the Tasman Sea, the result is a squash zone of enhanced
SE winds along 20 to 25 S this week, especially over New Caledonia.

Computers are picking that tropical Low should form on this SPCZ in
eastern Coral Sea around Wed 24 Nov and this should then deepen as it
crosses Vanuatu on Fri 26/Sat 27 Nov and weaken to south of Fiji by
Tuesday 30 Nov. Avoid this Low and, if in Noumea, consider waiting out
this squash zone.

SUBTROPICAL RIDGE: STR.
That large High stationed at 35S to South of French Polynesia should go
off to 40South and fade away by Wed 24 Nov.

A new high is filling the Tasman Sea during Monday 22 Nov. This should
hold itself there until it fades on Sat 27 Nov... and it should also
squirt a ridge across central NZ and Chathams Islands by Wed 24 Nov that
should go east around the south side of the Low near Kermadecs.

NZ AREA
Cool SW flow over NZ tonight (touch of snow in the Alps) turning
southerly on Monday 22 Nov.

The Stalled Tasman High keeps surrounding features away from NZ this
week, but a trough should be in place over Southland by the weekend in
readiness to move onto NZ early next week when the High fades.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 14 Nov 2010

2010-11-13T22:25:00.000-08:00

WEATHERGRAM
YOTREPS
Issued 14 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS Low 1006 hPa or less near 16S 176E or over NW Fiji this evening
Sun 14 Nov is moving SSE and should then move S then SW and fade near
Norfolk island from Tue 16 to Thu 18 Nov. Avoid the strong winds on
south side of this low and squally showers on its South and Southeast
sides. This means it is not the best week to sail from New Caledonia
to NZ.

The South Pacific Convergence Zone SPCZ has a branch from that LOW that
stretches off to the SE over Southern Tonga: this is weakening but
should wander east across Niue on Tue 16 Nov and Southern cooks on Wed
17 Nov. Another branch is building from east of Solomons towards Tuvalu
along 6 to 9S - this should gradually extend to Samoa and to Southern
Cooks during the coming week, with a drop in pressure. There is
another active branch north of French Polynesia FP between 11 and 17 S,
and models expect this to fade.

Coral Sea may turn into a breeding ground around 23 to 27 Nov.

SUBTROPICAL RIDGE: STR.
HIGH is expected to wander east over north of North Island on Mon 15 Nov
and then off to the east along 35 to 40S from Tue 16 to Sat 20 Nov when
it gets south of FP. There is likely to be a squash zone of enhanced
easterly winds along the north side of this High along 20 to 25S.

The SW flow that swiped over NZ today 14 Nov is likely to be injected
into the back of a trough south of Southern Cooks by Tue 16 Nov helping
intensify a LOW near 35S 155W that may then go through a rapid deepening
process and it shoots off to the SE.
Next High should wander east along 35S across the Tasman Sea slowly from
Fri 19 to Wed 24 Nov, and also have a squash zone of enhanced easterly
winds on its northern side over New Caledonia.

NZ AREA
A trough (the one that upset Tasmanian grand prix today) is expected to
stall over southern NZ on Mon/Tue/Wed 15/16/17 Nov making for a strong W
to NW flow over central and southern areas, and light winds for
Northland. Then a broad trough is expected to cross NZ slowly from
Friday 19 to Sun 21 Nov.

SAILING TO NZ -
SPCZ squalls and rough seas over southern Fiji and just south of Tonga
tonight and Monday.
Winds over Northland should be a useful NE to N from Thu 18 to Sat 20
Nov, then that weekend trough is likely to swing to wind to a SW/S from
Sun 21 to Wed 24 Nov -nothing major, but sailors may need to work out a
waypoint that positions them Ok for those SW winds early next week.

The HIGH SEAS email link I gave last week has suffered link rot. You
can get MetService HIGH SEA warnings via email to query@saildocs.com, no
subject needed, with message SEND
http://m.metservice.com/warnings/marine Or, for latest BRETT coastal,
SEND http://m.metservice.com/marine/coastal/brett.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 7 Nov 2010

2010-11-06T22:14:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 7 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The South Pacific Convergence Zone SPCZ is reasonably active and rather
scattered across the Coral Sea, but has weakened east of the dateline
(after being active there last week). During the coming week it looks as
though the SPCZ may weaken in the Coral Sea. A new zone may intensify
in the region from Solomons/northern Vanuatu to Samoa, then move south
towards Fiji and Tonga between 15 and 18 Nov. Be Aware.

A LOW in the subtropics developed near Raoul Island yesterday (Sat 6
Nov) and is moving slowly south along 165W ---it will generate big 3
metre plus SE swells and throw these onto the area between Tonga and
NZ, mainly around Raoul Island, until 13 Nov. This Low will block a
high in the Tasman Sea....

SUBTROPICAL RIDGE: STR.
HIGH is moving to east of NZ along 45S, but is expected to leave behind
a cell that will stall in the Tasman Sea, west of North island. This
stalled high cell will slowly wander to the north and is expected to
finally move east along 35S next week 15 to 18 Nov. There will be a
squash zone of enhanced SE winds on the north side of this HIGH, mainly
between 20 and 25S, from around southern Tonga to west of New
Caledonia, from 8 to 13 Nov ... but the winds near Minerva are likely to
be more from the South until 12th Nov.

NZ AREA
When the stalled HIGH left behind in the Tasman Sea wanders north from
wed 10 Nov, a NW flow should become established over the South Island...
wet for Southern Alps and warm dry winds for eastern South Island. All
OK.

TASMAN SEA
Next major trough should wander from Aussie Bight onto Tasmania on Sat
13 Nov with a low that should swing by Southland by Sun 14 Nov.

SAILING TO NZ???
The squash zone between 20 and 25S, and the southerly wind and 3 metre
plus SE swell near Minerva and Kermadecs, are the challenges.
Winds near Northland are OK: expected to be SE 15 kt or less until wed
10 Nov then SW/W around 10 kt until Wed 17 Nov.

I will be UNAVAILABLE during 8-12 Nov. So, if you want an update for
your arrival, maybe it's a good idea to avoid arriving on those days.
You can get the regular HIGH SEAS forecasts via email to
query@saildocs.com, no subject needed, with message SEND
http://bit.ly/subtropic. Or, for latest BRETT coastal, SEND
http://m.metservice.com/marine/coastal/brett.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 31 Oct 2010

2010-10-31T01:25:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 31 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Welcome to the official start of the South pacific Cyclone Season.
Nothing expected this week. The South Pacific Convergence Zone SPCZ has
been going through an active period recently. It has cleared off Coral
Sea and New Caledonia but is still being strengthened by an upper trough
near Vanuatu and lies almost west-east between 12 and 15S from Rotuma
across Samoa and to Suwarrow, it then extends SE across Southern Cooks.
The upper trough is expected to cross Fiji on Mon 1 / Tue 2 Nov where it
may form a surface low for a time, and then it should weak and it moves
over Tong on Wed 3 Nov. This will likely encourage the SPCZ to come
southwards this week.

SUBTROPICAL RIDGE: STR.
We did indeed get a High well over 1044 east of NZ this weekend. It is
now weakening and migrating NE to east of NZ and that area should become
more zonal and high index by the end of this week with just a ridge left
over along 30S and a disturbed westerly flow further south.

The next High is wandering along 45S across the Australian Bight. Its
nose end is shovelling cold air north, but the showers are expected to
mostly clear in time for the Melbourne Cup on Tuesday. Anyway, this
High should edge NE wards, crossing Tasmania / 40s on Fri 5 Nov, and
tonguing itself onto North island /35S on the 6-7Nov Weekend, then
dividing into two parts on 8-9 Nov - one part moving off to east of NZ
along 40S, and the other stalled in central Tasman Sea at 35S. There
are squash zones of enhanced easterly winds on the north side of this
high.

NZ AREA
Between those highs, there is a replacement trough. This is currently
over Tasmania and, at present, includes a rapidly intensifying low
centre that is rushing off to the South. It's the same trough which
deluged the Melbourne derby yesterday. Anyway it is expected to cross
NZ on Thu 4 Nov, preceded by a strong NW flow over central and southern
areas, and followed by a crisp cool SW with showers that will last into
the start of the fireworks on Fri 5 Nov.

TASMAN SEA
As indicated in my previous weathergram, on 5 Nov a LOW is expected to
form off Queensland coast, it should move SE and deepen, reaching peak
intensity SW of Norfolk on 7 Nov, and then it should slow down and
wobble near Northland on 8-9 Nov - then wander to the east to north of
NZ by around 10 Nov (uncertain). Strong squash zone of enhanced winds
between this LOW and that HIGH to the South especially from 9 to 12 Nov.

SAILING TO NZ???
The High east of NZ will maintain an easterly flow until 4 Nov.
That trough crossing Northland on 5 Nov is followed by a period of SW
winds, but for yachts coming from Fiji or Tonga these winds will likely
only briefly get to 30S and so are just a minor irritation (they will
also bring SW swell - reducing the comfort factor).

Of more interest is that LOW from the Queensland Coast. The computer
models are not yet is agreement as to what it may do, so updates will be
needed. Avoid this LOW neat Norfolk especially on 6-7 Nov as that's
likely to be when it peaks.

As for the Northland coast; most likely (not yet certain) idea is that
LOW will bring a period of enhanced ENE on Mon Tue 8-9 Nov and then
enhanced SE to S winds on 10-11-12 Nov. This complicates all voyages
that may be planning to arrive in NZ in the period from 9 to 12 NOV.
The impact of this Low should clear away so that a new weather window
may start opening for good voyage from New Caledonia /Fiji/ Tonga to NZ
after 13th Nov.

A further complication is that I will be UNAVAILABLE during 9-12 Nov, as
I'll be attending to a MetService display at the Canterbury Show. So,
if you want an update for your arrival, maybe it's a good idea to avoid
arriving on those days.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 24 Oct 2010

2010-10-24T01:58:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 24 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

When the moon fades into its last quarter there may be a rising of
Pololo (or, in Fijian, Balolo). These coral worms choose this time of
the year to spawn. Ask the locals about them, may be fun to watch and
perhaps catch and cook.

LA NINA and the coming cyclone season
First, a recap on our weather zones: The weather engine starts with
energy from the sun. The warmest seas are near the equator and sun on
them causes evaporation which rises to form the Intertropical
convergence zone. Air rises as far as the tropopause and then travels
pole-wards. In the southern hemisphere a lot of this air sinks around
30S and returns along the surface as trade winds back to the equator---
this is the Hadley cell. The zone of sinking air is called the
subtropical ridge. Further south are the westerly winds of the roaring
40s. These weather zones move about, causing seasons. By the time we
get to the longest day, around 22 Dec, the subtropical ridge is usually
"following the sun" southwards and gets to around 40S. This is all part
of the annual cycle.

The second strongest cycle for seasonal weather is the ENSO = El Nino
Southern Oscillation (there are others). When the seas along the
equatorial Pacific Ocean are cooler than normal, as the are now, we call
it a La Nina episode. The weather engine turns over more slowly. The
peak upward motions in the Pacific occur over the Australian side rather
than the Peru side. This has the impact of, in the Southern Hemisphere,
encouraging the weather zones to go further south than normal. Already
the "anticyclones of summer" are reaching northern NZ, and there are
signs of an early start to the wet season in northern Australia. This
also tugs the South Pacific Convergence zone SPCZ to the south and west.

When we look at the sea surface temps, the Oceanic Nino Index ONI for
Sep was -1.0 and when we look at the weather maps the SOI (Tahiti to
Darwin normalised pressure difference) was +2.5. Both these point to a
La Nina that is already moderate to strong. The sub-surface temps in
the central Pacific are cool as well, so the consensus is that this La
Nina will continue through the coming South Pacific Cyclone centre.

NIWA has been able to come up with 8 similar cyclone seasons: Nov 1970
to April 1971 or 70/71, also 71/72, 73/74,75/76, 88/89, 98/99, 99/00,
and 07/08. Using these years as a guide, the forecast for the Nov 2010
to April 2011 season is for 9 to 12 named storms (9 is average). 3 are
forecast to reach at least category 3, and 1 is forecast to reach at
least category 4 (average winds near centre of 64 knots or more). The
Coral Sea and surrounding places west of 180 have an elevated risk of
Cyclone impact.

Although there appears to be a reduced risk for places east of 180, all
communities should remain alert and prepared. In the 8 similar seasons
chosen there have been some cyclone impact in southwest parts of French
Polynesia and in the Southern Cooks. During previous moderate to strong
La Nina's, cyclones have been able to leave the tropics and cross the
Tasman Sea onto southern NZ.

TROPICS (this week)
South Pacific Convergence zone SPCZ is rather spread out, active, and
wide, from the Solomons to Fiji to Northern Tonga and then stretches
southeast across Southern Cooks. There is an active upper trough just
NW of New Caledonia tonight Sun 24 oct. This should cross New Caledonia
on Mon 25 Oct, southern Vanuatu on Tue 26 oct, and then Fiji and Tonga
on Tue/Wed 26 and 27 Oct. Another upper trough is being picked by the
GFS model to cross New Caledonia on Sat/Sun 30/31 Oct. Avoid.

SUBTROPICAL RIDGE: STR.
On Mon 25 Oct a new, replacement, HIGH is expected to develop over NZ as
the older one wanders off to NE and fades away. This new High then
should migrate east along 40 to 45S--- that's further south than normal,
but there will still be an zone of enhanced trade winds on its northern
side - a weak squash zone-- mainly between Fiji/Tonga and NZ from around
27 Oct to 1 Nov. This will provide spirited and bumpy reaching
conditions.

NZ AREA
Another replacement trough is expected to travel NE across NZ on
wed-Fri, 27-28-29 Oct , stalling awhile over central North Island ...
light winds and showery. This should be followed by an intense high
migrating east along 50S, making for a broad zone of easterly flow
between tropics and NZ, that then rotates into a northerly flow in the
Tasman Sea. This is called low-index*.

SAILING TO NZ
Conditions are OK this week, if you are happy with the enhanced trade
winds on the way and if you dodge the squalls of the SPCZ and its
passing upper troughs. Too early to say much about next week yet,
but the weather pattern does seem to be becoming so much of a "low
index" that the next likely step may well be a deepening low in area
south of New Caledonia in first week of November. So it may be better
to leave early rather than linger.

* The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 18 oct 2010

2010-10-18T02:30:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 18 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.
I'm back in the office now from attending to a display for MetService at
the Waikato Boat Show over the weekend, but had to wait until tonight to
get any spare time to write this.

LA NINA
SOI (90 day) is now 2.2 and reasonably steady. This is a strong La
Nina, more than two standard deviations from its mean at present. More
on this in next few weathergrams.

TROPICS
South Pacific Convergence zone SPCZ is now in its normal October
position from Papua New Guinea to northern Vanuatu, then, weak at
present but hovering between Rotuma and Fiji, then move active over
northern Tonga and Niue/Southern Cooks.

An upper trough over South Coral Sea and New Caledonia tonight 18 Oct is
embedded in the upper westerlies rather than the surface trade winds, so
it migrating eastwards... it should activate the SPCZ over Fiji and
Tonga on Tue wed 19-20 Oct. On late wed 20 and during Thu 21 Oct, a
cold southerly / SW wind (from NZ) is likely to reach as far north as
Kermadecs, just as this upper trough reaches the Niue area and this
combination may deepen the pressure around Kermadecs, thus strengthen
the cold winds between NZ and Fiji Tonga for a day or so. Wait for this
to move on before sailing south.

SUBTROPICAL RIDGE: STR.
Remains of last week's BFH are 1028+ at 40S to south of French Polynesia
FP moving off to the east, maintaining good trade winds over FP, much
like last week.

High 1028 is expected to move east along 35S across New South Wales on
19 Oct and then slowly across the Tasman Sea to cross the Auckland area
on Sat 23 Oct, just in time for the NZ Labour Day holiday weekend. Also
in time to impact on this year's Coastal Classic, so that there should
be a good SW wind in Auckland for a spinnaker start on Friday and then a
fading left-turning breeze over night to challenge the heavier boats.
And as that High continue its eastward migration early next week, a
northerly flow is likely on Monday for the boats then returning to
Auckland.

This slow moving high is a good marker for those planning voyages from
Fiji or Tonga to NZ. Wait for that upper trough to pass by, and so
arrange to depart from Fiji on 21 or 22 Oct (or over weekend if you can
get Customs clearance) and arrange to depart from Tonga on 22-23-24-25
Oct period. The High is expected to be over 1030 and east of NZ from
24 Oct and will then have a squash zone of enhanced easterly winds on
its northern side, ending our departure window. With these voyages as
we sail south the high moves off to the east, so we need to time things
OK and arrange to reach Northland before the following trough and its SW
wind change. In this case that trough is likely to be delayed until the
end of the month, say around 30-31 Oct... but it's so far away this will
need to be updated both at the start and during the voyage.

Good voyages from New Caledonia to NZ or Australia are also on the menu
after that upper trough has got east of Noumea, say, around Wed 20
Oct--- there will be some squash zone impact on the north side of the
Tasman High but nothing major.

NZ AREA
There is a strong upper trough and associated thundery cold front
crossing South island on Tuesday 19 Oct and North Island to the
Kermadecs on Wednesday 20 Oct. On Thu 21 Oct, SW winds still likely to
still be strong and showery in the west, but should be easing. From
then on it's the Tasman High that commands proceedings.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 10 Oct 2010

2010-10-09T22:57:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 10 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

LA NINA
SOI (90 day) is now 2.19 and reasonably steady. This is a strong La
Nina, more than two standard deviations from its mean at present. We are
currently investigating analogue years - this investigation is still
being done with NIWA. A classic La Nina shifts the South Pacific
Convergence Zone to south and west of its normal Summer position---
this encourages cyclones in the Coral Sea area. Sea surface
temperatures in there are already warmer than normal, so the season may
start earlier than normal. More on this in next few weathergrams.

TROPICS
South Pacific Convergence Zone SPCZ is now in its normal October
position from Papua New Guinea to Rotuma to Samoa to Southern Cooks.
That surfacing upper trough (SUT) near Niue referred to last week,
managed to work westwards and activate some squalls about Fiji Tonga as
well as Niue over past few days--- First real rain for Fiji for a long
time and I think there may have been some jetstream assistance as well.
Anyway -it hailed in Sigatoka, and that's unusual. Maybe we can call
this an early start to the Fijian wet Season.

Another trough is on the map == this time it's a surface trough that
started off from the mid -latitudes and has been stretched out by a
jetstream between Australia and New Caledonia. It should cross Vanuatu
on Mon Tue 11-12 Oct and then Fiji/Tonga on Wed Thu 13 14 Oct and then
fade.

SUBTROPICAL RIDGE: STR.
Remains of last week's BFH Big Fat High is a centre near 1028+ at 40S to
south of French Polynesia FP moving off to the east, maintaining good
trade winds over FP.
High 1038 in south Tasman sea today near 42 S is shovelling some cold
air onto NZ, and has a squash zone with a little trough on top of it
near Brisbane. High is expected to split into two crossing the South
Island on Tue Wed 12/13 Oct - frosty! The western part should then head
NE for Norfolk and Kermadecs for the 16/17 Oct weekend, and the eastern
part should follow the path of last week's BFH and keep the trade winds
well supported over FP.

NZ AREA
The leading edge of the cold air being shovelled over NZ should cross
North Island tonight (sun 10 Oct). During Mon 11 and Tue 12 Oct the
trough associated with this air is expected to sharpen and form a low
between Northland and Kermadecs. AVOID. This low should then move SE on
Wed Thu 13 14 Oct. There's a ridge over central NZ mid-week and then
over the North island for the weekend. For South and central NZ, a
moist NW flow is expected for the 16 17 weekend.

Heading for NZ? Don't venture south of 25/30S until that LOW had gone
away - say, around Thu 14 Oct. Then try and time arrival to fit in
with a northerly flow over Northland early next week.

NOTE: I'll be unavailable 14 to 17 Oct, busy attending to MetService
display at Waikato Boat Show. So next weathergram may not be until Mon
18 Oct-or later.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 3 Oct 2010

2010-10-03T00:05:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 3 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

LA NINA
SOI (90 day) is now 2.15, up 6% from last week, so La Nina is just
getting stronger. It now has values not seen since 1988. NZ's NIWA
Institute will be meeting to consider what this means for the coming
cyclone season, and I shall hold fire with my comments until after that.

TROPICS
South Pacific Convergence zone is mostly found at around 10S, but did
take an excursion across the Coral Sea during last week-touching New
Caledonia briefly.

There is an upper trough over the Suwarrow to Niue area slowly surfacing
to south and east of its axis. It's thundery. Should develop a LOW to
east of the Kermadecs on Mon 4 Oct that will move off to the SE then
stall around Thu 7 Oct.. The tropical extension of the trough will
likely kill the winds over the Cooks this week, and may even turn the
surface winds to a weak westerly, along with cloud and rain. SO it
isn't a good week to "puddle jump" westwards from Tahiti.

SUBTROPICAL RIDGE: STR.
Big Fat High BFH 1038 in mid Tasman Sea tonight 3 Oct is expected to
wander slowly along 40S this week easing to 1030 by the time it gets to
around 170W around Thu 7 Oct, and then slide around the south side of
the LOW that will be blocking its way. Yes there is a squash zone of
enhanced easterly trade winds on the north side of this High. It is, at
present, Sun 3 Oct in the North Tasman sea between 25 and 30S - and
should wander east with the high. It isn't a major, but has been near
gale force about the Whitsundays over past few days.

Next High is not expected to be as intense of the BFH but is likely to
wander east along 35S. It should bud off Australia into the Tasman Sea
around Sat 9 Oct and slide across the north of North island by Wed 13
Oct.

NZ AREA
Between the aforementioned Highs there is to be a passing trough, it
should cross the NZ area on Thu 7 Oct to Sun 10 Oct, preceded by NW
flow, accompanied by a series of fronts and followed by come cool SW
winds. This front is expected to have only minor impact at 30S so it
you are in Fiji or Tonga and wish to sail to NZ and can arrange a voyage
around the back end of the outgoing High, and rendezvous with the front
on 9 Oct near 30 to 35S, then that should be a reasonable voyage to NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM 7 issued 26 Sep 2010

2010-09-25T21:49:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 26 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

LA NINA
SOI (90 day) is now 2.02, up 9% from last week, now over 2 standard
deviations from its mean so La Nina is just getting stronger.
During October I'll explain what this means for coming migration/
cyclone season.

TROPICS
South Pacific Convergence zone is showing signs of hugging 10S... This
seems to happen around any equinox and so is likely to stay this way a
while. However there are signs of it spreading southwards in the Coral
Sea.

A pulse of extra convection is making its way eastwards from Indonesia /
North Australia into the North Tasman Sea, assisted by a subtropical jet
Stream --- this is producing cloud at high and mid levels and these
should thicken into a surface trough that is likely to cross the North
Tasman Sea on Wed/Thu 29/30 Sep and fade over Kermadecs around Sat/Sun
2/3 Oct.

A similar trough may come and go around Southern Cooks during the week.

SUBTROPICAL RIDGE: STR.
High 1026+ between Northland and Kermadecs at present (26 Sep) is
expected to move slowly SE to 38S and get south of French Polynesia by
the 2/3 Oct weekend and intensify to 1038+. This will strengthen the
trade winds on its northern side into a yucky squash zone. So if you
intend puddle jumping from Tahiti westwards this week, set off early
before the squash zone arrives.

Next High is crossing Australia at present and should move across the
Tasman Sea just as a weak 1025 ridge along 34S from Thu 30 Sep to Sun 2
Oct, and then be reinforced and get to a 1032 Cell and wander along 40S
from 2 to 3 Oct and cross central NZ 3-4 Oct. A welcome change from
past few weeks. Should be good for anyone wanting to come to NZ so long
as you arrange arrival before the next trough strengthens in the Tasman
Sea, and that, at this stage, is looking to be around 7 Oct. Also,
there is likely to be a squash zone building over Tonga/Kermadecs from 3
Oct.

NZ AREA
Monday 27 Sep : NW strengthening
Tuesday 28 Sep : Front embedded in NW flow.
Wednesday 29 Sep : Front stalls over North Island, Low whizzes past
Southland.
Thursday 30 Sep : Front lingers North Island, SW flow establishes
elsewhere.
Friday 1 Oct : Southwest flow ahead of a High.
Saturday 2 Oct : Dying southwest flow ahead of a High.
Sunday 3 Oct: Lighter variable winds around High in central/E
Tasman.
So, at this stage looking OK for the annual CANANZ Kowhai cruise in
Hauraki Gulf.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 19 sep 2010

2010-09-19T04:38:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 19 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Tonight's write up is a bit later than normal as I'm just now back in Auckland after attending NZ Coastguard national Conference... they are a great bunch indeed!

LA NINA
SOI (90 day) is now 1.85, up 0.11 from last week, so La Nina is just getting stronger.

TROPICS
South Pacific Convergence zone is beginning to return to normal now, showing up and bubbly convection over Papua New Guinea and Coral Sea, and also in an extending line from NW of Samoa across to French Polynesia. It is expected to hold this position this week.

There is a conveyer belt/upper trough over inland Queenstown and this is expected to move out to the Tasman Sea on Mon 20 Sep. It should then fade, but its jetstream is likely to feed some more convection in the Coral Sea, worth avoiding.

SUBTROPICAL RIDGE: STR/ NZ.
It is interesting to note that the parameter I'm using to measure the strength of the Polar Vortex went negative on Thu 16 Sep-That's when the large High I mentioned last week came into play and intensified over the entire Australian Bight. This High also had a Southern Ocean Low to help form an eggbeater onto Tasmania and into the Tasman Sea and onto NZ.

Tasmania took the brunt last Thursday /Friday, then, during the weekend, squally showers brought power cuts to Wellington and Auckland, snow that collapsed roofs in Invercargill, and slips /flooding that caused clusters of road closures. As is the nature of the beast with squalls, not everywhere got hit, and the damaged areas were rather random. Swells in mid Tasman got to an estimated 8 metres last Thursday and peaked on west and south coasts of NZ on Friday night

It's not over yet, there's another couple of shovel-full of cold air for NZ, especially on Tuesday 21 and Wednesday 22 Sep. Another 8 metre burst should roll across southern NZ seas on wed 20 to 22 Sep and reach Chathams around Fri 24 Sep, but the swells in the Tasman Sea are expected to ease to more normal levels by Wed 22 Sep.

That high in the Aussie Bight has not ridged all the way to Antarctic ice-shelf so this isn't a classic polar blast, really it's a wintry entrée to the equinox. Around the equinox, the air along the Antarctic fringe is just starting to get some sunlight after 6 dark months--- it is at the coldest it ever gets , and the sun tends to stir this cold air so that, when encouraged by surrounding pressure systems such as a passing Southern Ocean Low, it gets dislodged northwards. In this case, the shovelling is continuing to be done by that Aussie Bight High.

However, that Aussie Bight high is too far south for the STR at this time of the year--- even in a La Nina year (which twigs the STR to the south), the correct latitide for the STR over Australia around the equinox is about 30-35S , sort of along the South Coast. I think this high got knocked south by that upper trough/conveyer belt that has been over North and Central Aussie over the last few days. SO I agree with the models, and they all take this Aussie Bight high and, slowly, shift it north to 30/35S by Thu 23/Fri 24 Sep so that some high cells ooze across the North Tasman Sea from Thu 23 Sep and over North Island on the 25/26 weekend.

Naturally the strong and sometimes squally westerly winds of the roaring 40s and equinoctial gales will continue unabated to south of this STR line, and reasonably useful trade winds are continuing to north of the STR line.

Taking into account the expecting easing of well in the North Tasman sea by Wed and then the high that is expected to cross the North Tasman and Northland area next weekend, it looks to be a reasonable time to sail to NZ this week.

An added advantage during the next week or so is the full moon. This peaks on Thu 23 sep - and that's the date of this years Sep equinox.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 ISSUED 12 Sep 2010

2010-09-12T02:31:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 12 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

LA NINA
I've been asked to supply some details about the strength of this La Nina... The Oceanic Nino Index ONI, which measures the difference from normal of Sea temperatures in the target area of the eastern equatorial Pacific (Steep) now has a 90 day funning mean of -0.6 == roughly the sea is on average that much cooler than its norm. The Atmospheric Southern Oscillation index SOI, taken from the pressure difference between Tahiti and Darwin, has a 90 day running mean of +1.64 (standard deviations). Both indicate moderate to strong La Nina conditions and the ocean and atmosphere are coupled in this.

TROPICS
South Pacific Convergence zone is beginning to return to normal now , showing up as bubbly convection over Papua New Guinea and Solomons, and as a shear zone of vertical convergence (a layer of trade winds near the surface topped by some vigorous W to SW winds) around Tokelau/Samoa to Tonga/Niue to Southern cooks/ Tuamotu.

The upper trough the marks the boundary of this shear zone is expected to drop to the surface around the Southern cooks/ Tahiti on Tue/Wed 14/15 Sep and then to move south-maybe-Southwest across the Southern Cooks Thu 16 to Sat 18 Sep. Anyone planning the west jump from Tahiti should take this into account - maybe delay a while.

The northern extension of a mid-latitude front that moved off North Island of NZ today is affecting New Caledonia tonight Sun 12 Sep, and should fade away over Kermadecs around Tue/Wed 14/15 Sep.

SUBTROPICAL RIDGE: STR
A BFH big fat high which is well supported aloft continues to dominate proceedings. Its central pressure is around 1038 tonight Sun 12 Sep near 36S 155W and should slowly wander east and ease to be around 1028 at 31S 133W this time next week 19 Sep. So the squash zone of enhanced easterly winds on its northern side is bringing vigorous easterly winds and rough seas between Tahiti and Niue - at least until that trough drops down around Tue 14 Sep, and even after that it will take a while for things to settle down.

Not the best week then for venturing westwards from Tahiti.

Next high cell in the subtropical ridge doesn't have much vertical support - it is budding off eastern Aussie now and will cross the northern Tasman Sea on Mon 13/Tue 14 Sept and fade over Kermadecs on wed 15/Thu 16 Sep.

The high after that is expected to wander east across the Aussie bight along 40/45S on Sat/Sun 18/19 Sep.. shovelling cold air from 55S to Tasmania .. not quite a polar blast but it'll be a wintery entrée to the equinox for SE Aussie.

TASMAN/NZ
A brief break on Monday and then another front on Tuesday 14 Sep UTC, with some heavy rain for western districts, and followed by a cold SW in southern districts.

After another brief break late Wednesday and then some roaring westerlies of spring, enhanced by a deep low in the southern ocean -- these should reach NZ for Thursday 16 and much of Friday 17 Sep, followed by cold SW flow on Sat/Sun 18/19 Sep.

So a voyage from Tonga to NZ departing early this week may encounter a weakening trough/ridge couplet around 30S and then some strong west to SW winds over Northland around 20 Sep, reasonably adventurous.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 5 sep 2010

2010-09-05T00:29:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 05 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
There is a strong Walker/Hadley cell combo across the Pacific equator,
with rising air strongest between Malaysia and Taiwan and sinking air
strongest over Fiji to French Polynesia.

The South Pacific Convergence zone SPCZ is looking normal along 10S
across Papua New Guinea/ Solomons, but fades off over Tuvalu and to
north of Samoa. It is expected to extend east at times this week as far
as Suwarrow.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds as far as 15S. One of these
brought some welcome rain to Fiji mid last week (not enough to have much
impact on their dominating dry spell). This has faded somewhat is should
wander east across Southern Cooks on Mon 6 Sep and southern parts of
French Polynesia on Tue 7 and Wed 8 Sep. It is followed by a period of
strong trade winds with a bumpy south to southwest cross-swell. The
next such trough is likely to cross the North Tasman Sea and reach New
Caledonia on Sat 11 Sep.

SUBTROPICAL RIDGE: STR
A big fat high with central pressure over 1030 is moving east along 30S.
It has a squash zone of enhanced trade winds on its northern side over
the next few days. Tonight, Sun 5 sep it is over the dateline.
On Thu 9 Sep it should have wandered east as far as 160W, to south of
Southern Cooks, where it will be reinforced by another High wandering
along 35/40South and the combo high should get to way south of French
Polynesia on the Sat/Sun 11/12 Sep weekend.
Yes, this high is enjoying some of that curtain of sinking air referred
to above in the combo Walker/Hadley cell combo.

TASMAN/NZ
The Tasman Sea/NZ area is slowing moving into a long wave ridge area
after being under the influence of an upper trough for weeks. Even so
there is one more low to come ... This is the one that flooded Victoria
late last week and on Saturday (some places getting heaviest rain in 50
years). Its Northwester and front is crossing most of NZ tonight and on
Mon 6 Sep - heavy rain for Southern Alps and gusty east of the divide.

The low itself should follow and is expected to split into two across
central NZ on Tue 7 Sep--- that will allow a cold southerly to possibly
bring rain/sleet/snow to southern NZ on Monday night to Tuesday night,
and may be some heavy rain to Bay of Plenty during Tuesday.

Thanks to the new long wave ridge, these lows are likely to fade on Wed
8 Sep as a new HIGH crosses southern NZ, but this does bring onshore
flow and rain to eastern North Island.

On Thu/Fri 9/10 Sep, as that new High moves off, a northerly flow is
likely to develop over NZ, but there may be a trough over the North
Island. Then the forecast is for a front on Sat 11 Sep followed by a
westerly flow on Sun 12 Sep. The outlook next week 13-18 Sep is for
West to southwest winds over Northland, so those days may not be good
days for sailing towards NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 29 Aug 2010

2010-08-29T02:11:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 29 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The South Pacific Convergence zone SPCZ is strong along 10S across Papua
New Guinea/ Solomons and Tuvalu, and is likely this coming week to
extend to Tokelau, and maybe even affect Samoa to Suwarrow at times,
but otherwise is weak.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds as far as 15S. One of these is
expected to affect Fiji on Mon 30 Aug (some welcome rain!) Tonga on Tue
31 Aug, and then fade on its way to Southern Cooks by Thu 2 Sep.
Apart from this interruption, it looks to be a good wind for trade
winds in South Pacific.

SUBTROPICAL RIDGE: STR
Something to do with some extra energy in the subtropical jetstream
above around 30S. So the High that is expected to reach Lord Howe Island
by Wed 1 Sep should anchor its stern there and then rapidly extend
eastwards along 25/30S so that its nose gets to south of French
Polynesia by Fri 3 Sep. This is in response to a curtain of sinking
air, and it helps to feed the trade winds at 15 to 20S over the entire
region.

Next HIGH in the Tasman should build east of Sydney around Friday 3 Sep,
in good time to cross the North island during the 4/5 Sep weekend J

TASMAN/NZ

The long wave trough that has been bothering the Tasman sea is
retreating north for a bit. There is still a haphazard procession of
fast moving fronts bothering Tasman /NZ but the distance between troughs
is getting more, allowing for some voyage planning. And there may be a
break in this with next weekend's passing High.

Before then, today's trough is expected to settled into a couplet of
lows east of the North Island on Mon 30 Aug to Wednesday 1 Sep (stand
by for some rain in the Hawke's Bay ranges). The next trough is likely
to be preceded by a vigorous NW wind over South Island on Thu 2 Sep and
followed by a disturbed SW/S flow on Friday 3 Sep.

Anyone intending to head south to NZ this week can probably find
reasonable weather so long as an arrival around 6 or 7 Sep is targeted.
Plenty of south/southwesterly winds for anyone heading North, but avoid
the prefrontal conditions on Thu 2 Sep.

The parameter we use to measure the strength of the polar vortex has
indeed gone negative in the past few days, first time since May. This
increases the chances of a polar outbreak somewhere ... and indeed there
seems to be one near the Horn this weekend, but none, so far, anywhere
else.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 22 Aug 2010

2010-08-22T00:53:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 22 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The South Pacific Convergence zone SPCZ is slowly returning to normal
over Papua New Guinea and Solomons. It is putting in an appearance
around Tokelau, but otherwise is weak . Should continue to rebuild
from Tuvalu to Northern Cooks this week, and may start to drift south
for a while next week.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds as far as 15S over French Polynesia
and as far as 20S elsewhere. One of these is moving east off French
Polynesia today 22 Aug, and another should cross Tonga on 23 Aug, Niue
on 24 Aug, Southern Cooks on 26 Aug, and French Polynesia around 28-30
Aug. SO this week is something like a repeat of last week.

SUBTROPICAL RIDGE: STR
Upper air is such that Subtropical highs are being encouraged in north
Tasman Sea and in the broad zone east of NZ. There is a high cell in the
North Tasman Sea today 22 Aug: it should cross NZ on Tues 24 Aug and
then wander to the east slanting to 35S then 25S and reaching 150W to
South of French Polynesia by Sat 28 Aug. There should be a squash zone
of enhanced trade winds on the northern side of this high.

TASMAN/NZ
Weak frontal system is likely to cross NZ on Wed 25 Aug after that High
- preceded by a northerly flow and followed by a westerly.

A long wave upper trough is hovering around the Tasman Sea again this
week.

At ground level, we have a broad cold trough and a deep southern ocean
Low located today well to south of West Australia at 150E. This system
is the highlight of the coming week. Its Low centre should start moving
NE out of the southern Ocean when it gets south of Tasmania on Wed 25
Aug and reach NZ on Sat/Sun 28/29 Aug. However, there the High
following this system and it is expected to expand at 30 to 35S over SE
Australia on Sat /Sun 28/29 Aug. So that will limit the southerly fetch
this low can draw on, so it'll be wet and windy, but not a polar
outbreak.

SO it is OK to approach NZ until Tue 24 Aug. Then not OK until around 2
Sep.

The strength of the polar vortex was mentioned last week. Well, its
still holding its strength and is not weakening as much as the computer
models have been picking. Even if it does weaken to a stage that a polar
outbreak can occur in early September, the chance that this will impact
on our quarter of the world will be 1 in 4. So, while it is interesting
to watch for, it ISN'T another thing that yachties who are planning a
voyage from tropics to NZ or Australia need to worry about.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 15 Aug 2010

2010-08-15T02:21:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 15 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The causative factor for the cold air that brought floods to Pakistan
and slips to China AND the hot air bringing heat waves to Russia is the
same: meanderings in the Northern Hemisphere's jet streams. Over the
past few days NZ copped a burst of water vapour that had come from the
monsoon area, and this brought something like 200 to 300mm rain to our
mountains with some flooding and slips most notably around Whakatane,
but some drier air is now separating Asia and South Pacific.

The South Pacific Convergence zone SPCZ has faded recently over Papua
New Guinea and Solomons - should rebuild there by 20 Aug. It has built
up along 10S between Tuvalu and Tokelau, and is likely to slowly spread
south possibly affecting Rotuma to Samoa by Friday 20 Aug.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds along 20S. One of these is moving
east off the Tuamotus today 15 Aug, and another should cross Tonga on
16 Aug, Niue on 17 Aug and Southern Cooks on 18 Aug. Then the
subtropical ridge may be strong enough to block any northern extensions
of mid-latitude troughs, for a while anyway.

SUBTROPICAL RIDGE: STR
Small high cell in the north Taman Sea today 15 Aug is expected to move
east along 25S and fade near 180 on Mon 16/ tue 17 Aug. Next High will
be larger, forming in Tasman Sea on Wed 18 Aug and then moving east
along the 25 to 30S latitude band, reaching 180 around Fri 20 Aug, and
likely to be south of French Polynesia around Sun 22 Aug. There should
be a squash zone of enhanced trade winds on the northern side of this
high.

TASMAN/NZ
A long wave upper trough is hovering around the Tasman Sea this week.

At ground level, a broad cold trough, with squally thundery showers, is
now crossing the Tasman Sea and should cross NZ on 16 and 17 Aug.
Its SW flow is likely to linger over NZ on Wed 18 and much of 19 Aug.

Most settled day this week is looking to be Fri 20 Aug - for anyone
contemplating sailing to or from NZ.

Another broad cold trough is expected to cross Tasmania around Thu 19
Aug and reach the South Island on Sat/Sun 21/22 Aug.

There is a parameter that measures the strength of the polar vortex
(that ring of westerlies than encircles Antarctica). It is called the
AAO and can ne seen at
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/
aao_index.html - and known locally as SAM (Southern annular modulus).
Not usually relevant here, but has been way out of whack recently with
record high values, up to 4 standard deviations from its mean last
month. This suggests that Antarctica's cold air has recently all been
locked up, no polar outbreaks anywhere. Well, computer modelling is
suggesting this will all change by end of August, and then polar
outbreaks will be on the menu again (not sure which longitude band yet).
--

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 8 Aug 2010

2010-08-07T23:03:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 8 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
More heavy rain is forecast in the Monsoon over Pakistan this week, and
lots of rain over much of Indonesia. A conveyor belt directed some
moisture from there to NZ over the past few days. If you have access to
Internet see this at http://www.ssec.wisc.edu/data/comp/wv/wvmoll.mpg

The South Pacific Convergence zone SPCZ is strong about the Solomons and
somewhat quiet elsewhere. It is expected this week to build in the
Tuvalu and Tokelau area, and this may spread towards Samoa by the end of
the week.

Passing troughs in the mid-latitudes are extending far enough northwards
to affect the southern parts of the tropical South pacific, but not to
reach the SPCZ. One of these is located south of Fiji tonight and
should wander east and reach Southern Cooks by Thu 12 Aug UTC...
Preceded by a swing of the trade winds so they come from the NE,
accompanied by some squally rain, and followed by southerly winds and
clearing weather. Another of these troughs is expected to form off the
east coast of Queensland on Tue 10 Aug and wander east across the Coral
Sea to reach New Caledonia by Thu 12 Aug. If sailing, try and plan
around these troughs - at least remember that the computers and GRIB
data can not resolve the details near them.

SUBTROPICAL RIDGE: STR
Long wave pattern continues to be conducive to forming troughs in the
Tasman Sea and helping the STR in longitudes east of the dateline.

The HIGH forming now/8 Aug UTC over western Tasman Sea is expected to be
rather slow and weak until it crosses northern NZ on Wed 11 Aug and then
should expand east of NZ until Sat 14 Aug. There is likely to be a
zone of enhanced trade winds on its northern side.

TASMAN/NZ
A southerly start to the week with an outgoing low- barometers are
rising. Rain was briefly intense on Saturday and there are still some
intense showers around- in Wellington slips are disrupting traffic.

Fronts following Wednesday's high are likely to cross NZ on Thu 12 and
Fri 13 Aug, followed by a low that may linger over Northland for the
14/15 weekend.

So it is OK to sail towards Northland if you can get there by
Wednesday, and anyone planning departure should consider waiting until
next week.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 1 Aug 2010

2010-08-01T00:27:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 1 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
Asia is much wetter than normal, and in true Walker circulation style
this extra rising air is producing more sinking air in the subtropics,
accentuating the subtropical ridge especially around the eastern Indian
Ocean and Western Australia.

The South Pacific Convergence zone SPCZ has been knocked a little south
by this so that it has been DRY recently over Vanuatu, Fiji, and from
Samoa to Tahiti, and wetter than normal from Coral Sea to south of Niue,
with trade winds much stronger than normal over the whole South Pacific,
especially about Coral Sea where it is being drawn into a strong
Monsoon.

A passing upper trough in the mid-latitudes is likely to help accentuate
the SPCZ between Samoa and Southern Cooks on 2 Aug (UTC). There should
be some squally showers in this trough as it crosses Southern Cooks
around 3 Aug and Tuamotus by Thu 5 Aug. This offers something for the
puddle jumpers at Tahiti to take into account.

SUBTROPICAL RIDGE: STR
Long wave pattern is conducive to forming troughs in the west Tasman Sea
and helping the STR in longitudes east of the dateline.

The Large HIGH over 1036 east of NZ today (1 Aug) is expected to wander
east along about 40S this week, with a Low forming on its northwest
shoulder near 30S 150W around Tue 3 Aug UTC. As this pair wanders off to
the east, some smaller High cells are likely to form near latitude 30S
about and east of NZ by Fri 6 Aug, with fresh to strong trade winds on
their northern side.

TASMAN/NZ
One Low deepened in the mid Tasman Sea on 31 July and is expected to
track SE across Southland tonight. Next Low should deepen off New South
Wales on Mon 2, rotate clockwise around the Tasman Sea and weaken into a
trough that is likely to cross NZ on Wed 4 Aug UTC. Third Low should
deepen rapidly over Tasmania on Wed 4 Aug and rotate clockwise around
the Tasman Sea and cross North Island around Sat/Sun 7/8 Aug UTC.

There are brief ridges with slack winds between these lows but generally
too brief to allow much planning for a sail trip to or from NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 25 July 2010

2010-07-24T23:55:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 25 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence zone SPCZ is mainly along 8 to 11 South from
Solomons to Tuvalu/Tokelau. It occasionally peels away to the southeast
and makes a trough-an example of this should occur over Tonga Niue on
Sat 31 July, and this may develop into a LOW to south of Southern Cooks
early next week.

Passing mid-latitude trough occasional extend north in to the tropics.
As they pass, the trade winds weaken and get swung to be from the NE for
a while, then squalls appear, sometimes followed by a swing to southerly
winds. One of these events is near Niue tonight and should wander east
across Sothern Cooks by Tue 27 July.

SUBTROPICAL RIDGE: STR
This is stronger than normal now and further south than normal, signs of
an incoming La Nina.

HIGH 1034 budding off New South Wales on Mon 26 July should wander along
35S crossing northern North Island around Thu 29 July and reaching 150W
by Sun 1 August. A Squash Zone of enhanced trade winds is likely on
north side of the High, mainly between 15 and 10S, reaching Samoa on
Tuesday/wed 27-28 July. This squash zone is especially strong in mid
Coral Sea and across northern Vanuatu until Wed 28 July. Avoid.

TASMAN/NZ
With the incoming High, NZ is in a disturbed West to Southwest wind
flow, with fronts, on Monday/Wednesday 26-28 July; OK to good for
sailing off to the north.

After the Thursday HIGH, a disturbed flow from the NW is to be expected
over NZ, and this should wetten the West Coast and warm the East Coast,
and lead to a LOW crossing the South Island on the 31/1 weekend; good
for sailing towards Northland from the tropics, but please note this
good window closes quickly by Sun 31 July.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 18 July

2010-07-18T03:02:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 18 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence zone SPCZ is showing signs of drifting south
after a few weeks of hovering along 10S to 14S. One branch extends from
Solomons to Wallis/Futuna, and another branch is hovering between 10 and
14S between Tokelau and Samoa and around Northern cooks.

The SPCZ is occasionally enticed southeastwards to merge with
mid-latitude troughs. As this combination wanders east along around 20S
it swings and then kills the trade winds for a day or so, but that's
about all this week.

For those in Tahiti looking to go west: One of these troughs is
expected to pass by Rarotonga on Mon 19 July. The next is departing
Queensland at present, should pas by New Caledonia on wed 21 July, Tonga
on Sat 24 July and Rarotonga around Tuesday 27 July. Otherwise this is
a week of trade winds.

SUBTROPICAL RIDGE: STR
A lot can be gleaned by watching the rhythm of the highs as they wander
east in the subtropics. Their shifting isobars mould the troughs
inbetween them.
This week the STR is becoming better defined in the pacific than it has
been for awhile.

One High with central pressure around 1025 is wandering along 30 to 35S
, across Northern North Island on Mon 19 July, then slowly and steadily
east or southeast to get to 40S well to south of French Polynesia around
Friday 23 July. This High is mediocre, so will maintain moderate trade
winds and settled weather in the tropics on its northern side. Good for
sailing to the west.

Next High is likely to be more intense, building to 1035+ between 35 and
40S in South Tasman Sea around Mon 26 July. Too far away to be sure,
but this high is likely to cross central NZ on Wed 28 July and should
have a squash zone of enhanced trade winds on its northern side - and
these strong winds will likely start in Coral Sea from Wed 21 July and
spread east to reach Vanuatu/New Caledonia by weekend of 24/25 July and
further east next week. Be wary.

TASMAN/NZ
It is between the highs that the lows can flourish, scrum together, and
elbow outwards.

There's a trough departing the Australian eastern seaboard tonight (18
July) and as this trough crosses the Tasman Sea on Monday/Tuesday 19/20
July a Low is forecast to form within it. This low will likely have
colder than normal air in its upper parts and that help to deepen its
central pressure, slow it down and breed squally showers/strong
winds/heavy swell. It may deepen to below 995 while still west of the
North Island on Wed 21 July. Avoid. Should then start to weaken , but
may still be around 1000 hPa as it crosses North island on Friday 23
July, and then it should wander off to southeast of NZ and expand to
cover the broad area between the two highs mentioned above.

So anyone sailing to NZ should best arrive by Tue 20 July, and this
isn't the best week to depart NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 11 July 2010

2010-07-11T00:18:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 11 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence zone SPCZ is still quiet but slowly activating
along 10S from Coral Sea, in clumps, all the way to Northern Cooks and
Marquesas. It has been hugging to 10S latitude, but occasionally links
south with mid-latitude fronts, making wet troughs --- one affected the
Cooks on 7 and 8 July and another affected Fiji on 9 and 10 July. This
latter trough is expected to continue eastwards and finally fade out
between Cooks and Marquesas on 15 and 16 July Thu/Fri. Anyone heading
west from Marquesas to the Cooks, or south from Tonga or Fiji to NZ will
need to factor this trough into their plans.

There is a low; lets call it L1, which has formed with the trough that
was over Fiji last night. This Low is near 30S 180 and should move
steadily south along the 180.

Total Eclipse: Clouds seem to be keeping away from the area that will
become a total eclipse at 111830UTC near Maria Island in the Tuamotus
(and Mangia Island in the Southern Cooks). Easter Island is currently
partly cloudy and clearing, but there is a cloak of cloud heading that
way, so fingers crossed there.

SUBTROPICAL RIDGE: STR
High over 1030 crossing NZ this weekend is likely to wander off to the
east between 40 and 45S getting as far east as 140W by the end of this
week. This is so far south that it isn't likely to enhance the trade
winds on its northern side-but there will be a squash zone between it
and L1 that is worth avoiding.

Next high upstream will be slow to appear, and is likely to bulge east
off southern Queensland around Fri/sat 16/17 July, stretching east along
25/30S to get to 180 by Tue 20 July. This northern latitude STR will
help enhance a westerly flow over NZ.

TASMAN/NZ
Yes, we got polar air over NZ this weekend, as mentioned in the previous
weathergram; it was mainly dry but did manage to bring us the lowest
temperatures we have seen this winter.

As L1 comes south over next few days, the eastern North Island are
likely to get a dose of cold southerly rain, especially on Wednesday
/Thursday 14/15 July.. But the low should be further away than last
week's, and hopefully will have less impact.

There are some nice tail winds around L1 for anyone wishing to sail
northwards from Northland. These winds will fade away by Wednesday and
then turn northwest and then strong westerly for the remainder of the
week.

A winter /Southern Ocean Low is expected to deepen off Tasmania on Wed
14 July and then head northeast out of the south Tasman and onto the
South island / central NZ on Sat 17 July, followed by a disturbed
southerly and then a Southwest flow.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 4 July 2010

2010-07-03T23:41:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 4 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: It seems this week that the direct route using
the current near 4South is NOT any faster than the alternative route
using the strong west-going current at around 2 degrees North from 100
to 120W. If you do decide to take the northern route you have to get
away for the east-going current at the equator, and you will likely
experience some squally showers.

TROPICS
South Pacific Convergence zone SPCZ is reasonably quiet this week, and
is mainly in the northern Coral Sea and northern Vanuatu and from there
along 10S towards Tokelau and Northern Cooks. There is an interesting
dry slot of sinking air from Fiji to Southern Cooks, and another around
northern Australia.
Due to High pressures that are now blocked over southern Australia there
is a zone of enhanced trade winds in the Western Coral Sea and around
the north end of Queensland. This should ease after 7 July but isn't
going to go away this week.

SUBTROPICAL RIDGE: STR
High to east of NZ today Sun 4 July is set to move steadily along 30S
and fade on 5 July. Another associated High should expand at 45S -50S
and this High fades This High should then move NE and reach 40S to south
of French Polynesia around Fri 9 July, with a squash zone of enhanced
trade winds on its northern side.
Next high upstream is stalled over South Australia but should be able to
send a cell across Tasmania on 8 July, South Tasman Sea on 9 July, and
South Island on 10-11 July.

TASMAN/NZ
This week the NZ region will be dominated by a large slow-moving low.
It isn't expected to ingest any cold polar air until 9 -10 July and by
then should be mostly off to east of NZ. The centre is expected to
track east along 33S to 180 and then southeast, so that most of its wind
and rain should stay out to sea, but Gisborne and Hawke's bay are in for
steady rain from Monday to Wednesday. The SE winds associated with this
low should cover northern NI tonight/Monday and central/southern North
island on Tuesday and Wednesday 6-7 July.

The low should be far enough away to allow reasonable sailing to the
north again by Thu 8 July. There is likely to be a left-over trough
between NZ and Fiji and this may activate early next week, so updates
will be needed.

As for sailing from Tonga to NZ, well : there may be a reasonable voyage
afte the low has gone, starting around 9 July, but you will need to be
prepared to sail through a trough.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 27 June 2010

2010-06-26T20:57:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 27 June 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: trade winds are now strong enough so that boats
faster than 6kt may sail this route directly, hugging 4S as long as
possible. Slower boats and those looking for an alternative route
should get to may between 1 deg and 2deg North of the equator for a free
ride on the equatorial west-going current, especially from 095 to 125W.
No weather to mention, but note that in the Northern hemisphere near
the Americas Cyclone CELIA is still going and Cyclone Darby is about as
well.

TROPICS
South Pacific Convergence zone SPCZ is active along 8 to 10S across the
Solomons area to Tuvalu and Tokelau, and then active again across French
Polynesia. There are occasional bursts of activity occurring about
northern Vanuatu and northern Fiji, but nothing organised.
Due to High pressures that are now blocked over southern Australia there
is a zone of enhanced trade winds in the Western Coral Sea and around
the north end of Queensland. This should ease after 30 June.

SUBTROPICAL RIDGE: STR
Large HIGH over 1030hpa to south of southern cooks / at 160W / is moving
steadily east along 40S. Its associated squash zone of enhanced trade
winds should affect southern parts of French Polynesia this week.

Small HIGH around 1020hPa is moving along 25S and should get from south
of New Caledonia today to south of Niue tomorrow/28 June. Another small
High around 1020hPa is likely between 25 and 30S to south of New
Caledonia on 29 to 30 June , and should then fade.

And the next HIGH is likely to bring a period of light winds across the
central Tasman Sea and NZ building to 1030+ from 5 to 7 July next
week...- a window that motor vessels may use to help cross the ditch as
comfortably as possible (and sailing vessels may wish to avoid).

TASMAN/NZ
This week in the local region we have just two small cells in the STR
around 25/30S, so the whole Taman Sea/NZ /east of the dateline area is
open to having a broad trough.
There should be one front/trough crossing NZ on Monday/Tuesday 28/29
June, followed by a disturbed W/SW flow for the remainder of the week.
After this SW wind change gets to Northland on wed 30 June, there should
be a reasonable window from sailing away from Northland. BUT note that
the frontal trough may deepen into a small low when it is north of NZ
and as it crosses near the Kermadecs on 2-3-4 June-so if heading for
Tonga ensure you go clockwise around it.

These conditions will make sailing TO New Zealand challenging this week.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 ISSUED 20 June 2010

2010-06-20T02:30:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 20 June 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: trade winds are now strong enough so that
anyone sailing this route may as well go direct, rather than chase the
extra help of the west going current that is around 30 miles north of
the equator. Head for 4S and then hug that latitude to 120W - that will
avoid a counter just west of Galapagos and prolong time in a west going
current near 4S. No weather to mention, but note that early this week
there are TWO cyclones in the NE Pacific, BLAS and CELIA.

TROPICS
South Pacific Convergence zone SPCZ is building in activity. It spent
last week over Coral Sea/Vanuatu, Fiji, and Samoa, then weaker between
Northern and Southern cooks, then strong again over French Polynesia FP.
It should reform slightly further north over Tuvalu and Tokelau this
week, and some of the convection in the SPCZ is likely to be drawn to
the SE by passing mid-latitude troughs - so look for troughs turning to
lows in the subtropics at around 20 to 30S from Sat 26 to Sun 27 June:
one near 180 and another near 120W/ SE of FP.

SUBTROPICAL RIDGE: STR
The squash zone and heavy swells over FP on Sun 20 June are related to a
HIGH at 40S, to Southeast of FP. As this wanders off to the east it
will take its squash zone with it.

HIGH crossing Tasmania on Tue 22 June should go east and get across
South Island on wed 24 June and then should slide northeastwards and
reach 30S to south of FP by Monday 28 June. cross the Tasman Sea on
Tue/Wed 15/16 June, and North Island on Wed 16/Thu 17 June, and then
slide off to the NE and get to move smartly along 40S to be south of
French Polynesia by Mon 21 June. Its migration to the east will be
accompanied by a squash zone in the trade winds on its northern side,
mainly along 20S. There will be a squash zone with this High, but
mainly on its NW shoulder.

Next HIGH is likely o be delayed getting across Australia and, at this
stage, is expected to reach Tasmania around 1 July - so next week, with
no Subtropical ridge around NZ, the stage is set for a large LOW over or
east of NZ.

TASMAN/NZ
Disturbed W/SW flow over NZ is good for those wishing to sail off north
today/Monday/Tuesday 21/22 June, but on wed 23 June an SE change is
likely to reach northland. This will be counter productive to sailing
and, combined with the movement of the High to the South Island is
likely to result in the formation of a LOW that may loop and linger
around Northland for the remainder of the week.

The next good sailing window from Northland will then be after this low
has moved sufficiently off to the east - probably Mon or Tue 28/29 June.
And that low is likely to deepen and expand in area as it goes east,
because of the weakness of the STR. If you are interested in this
window, then be aware that it may be bothered by lows and troughs
lingering around 30S, so re-check closer to the time. Also, around 1
July, between the expanding low to the east and the incoming High in the
South Tasman Sea, there should be a polar outbreak with cold
southerlies over NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 13 June 2010

2010-06-13T03:38:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 13 June 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: Apparently some are still "puddle jumping"---
There is a good west going current to be found at around 30 miles north
of the equator . Take this to around 123 W and then head direct for
Marquesas. Weather is looking settled this week.

TROPICS
South Pacific Convergence zone SPCZ is active mainly in the Eastern
Coral Sea, with scattered areas along 10S near Tuvalu to Tokelau/Samoa.
This week the convection to north of New Caledonia is expected to drift
east, and form a trough to east of New Caledonia. Around Wed 16 June a
low should start to form in this trough and then deepen and travel SE
to east of North island and South of Kermadecs by Sat 19 June. There
will be a squash zone between this LOW and a HIGH over NZ on 16 -17
June.

Anyone taking the opportunity to sail north from NZ when the SW winds
start easing on Mon 14 June and heading for Fiji or Tonga should ensure
they go clock-wise around this low and its squash zone.

SUBTROPICAL RIDGE: STR
HIGH should cross the Tasman Sea on Tue/Wed 15/16 June, and North Island
on Wed 16/Thu 17 June, and then move smartly along 40S to be south of
French Polynesia by Mon 21 June. Its migration to the east will be
accompanied by a squash zone in the trade winds on its northern side ,
mainly along 20S.
Good to see this pattern return, as it is the regular winter pattern.
That LOW mentioned as forming in the tropics will probably wait for this
High to get out of the way first.

Next HIGH may be delayed and knocked to 45S and move into South Tasman
Sea south of Tasmania on 22 June.

TASMAN/NZ
The arrival of the Wed/Thu High coincides with the start of the National
fieldays which I will be attending this week. Fog and frost will be on
the menu.

A front should cross NZ on Fri 18/sat 19 June following this High, but
this is expected to fade as it comes, so will not bring a SW change to
Northland.

A Low is forecast to form off the Queensland coast on Fri 18 June, and
this should move SE across the North Tasman Sea and then across
Northland around Tue 22 June Tuesday. This LOW may or may not be
able to time its arrival along with the outbreak of cold southerlies
that will be shovelled onto the South Island by the next HIGH. So NZ
may be in for another cold S/SE outbreak early next week.

This means that the NEXT SW wind change in Northland for good sailing
to the North has been delayed to maybe the end of next week /maybe the
end of the month. Tomorrows "window" closes quickly too.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 6 June 2010

2010-06-06T00:59:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 6 June 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Whoops - I see that last week's email heading was dated 30 July 2010
instead of 30 May 2010.

TROPICS
South Pacific Convergence zone SPCZ is still gradually reforming along
10S, from Papua New Guinea to east of Solomons to Tuvalu/Tokelau and
extending to Samoa at times, also extending south between Vanuatu and
Fiji at times. During this week it seems that there will be more
convective activity building in the Coral Sea, and this may culminate in
a trough/low forming west of New Caledonia by around 19 June (end of
NEXT week).

There has also been more rain clouds than normal in a zone from just
south of New Caledonia onto northern NZ . This zone isn't part of SPCZ,
rather it is a combination of the northern end of mid-latitude frontal
systems + jetstream intensification + a large upper low stuck in the
western Tasman Sea and developing a series of surface lows to throw at
NZ, like a bowler player cricket. This "low index" pattern started in
mid May just in time to harass this years Auckland to Fiji race. It
seems to me that the pattern is about to change this week to the more
familiar "Roaring 40s" pattern.

SUBTROPICAL RIDGE: STR
The STR has been absent over NZ since mid May. There have been thin
ridges squeezing along 20 to 30S - north of the normal latitude, making
for lighter than normal trade winds between Fiji and French Polynesia.
This is about to change. The next STR is over central New South Wales
today (sun 6 June) and should wander east between 30 and 40S, crossing
NZ on Wednesday 9 June, and then settle between 25 and 35 South as it
wanders east of NZ.

The following STR should be a large HIGH in the Aussie Bight on Fri 11
June. As it crosses Bass Strait on the weekend of 12 /13 June it should
shovel polar air onto southern NZ producing a solid dump of snow there.
Models indicate this High will not be able to get into the Tasman sea at
40S , so it should go N across eastern OZ on 14/15/16 June and then
move east along 30 to 35S - across northern Tasman sea and north of NZ
on 17/18/19 June--- with enhanced easterlies on its northern side and
enhanced westerlies on its southern side --- the "Roaring 40s" will be
back.

TASMAN/NZ
Low crossing central NZ on Monday should go southeast across Chathams on
Tuesday. There is a sting in its tail, as one more squally trough with
W to SW winds is expected to be crossing northern NZ on Tuesday as well.

Light winds with a ridge on Wednesday.

Trough/front is expected to move from Tasman Sea across NZ on Thursday
and early Friday. The SW winds following this trough should reach
Northland Friday morning, producing a reasonable looking window for
sailing northwards.

Additionally, there is a brief window late Tuesday and early Wednesday,
with the minor impediment of some pre-frontal northerly winds on
Thursday and - note well- following the Friday front - there is
expected to be a period of heavy westerly swell over the seas north of
Northland.

I'm gearing up now to attend to MetService display at Fieldays from Tue
15 to Sat 19 June. There should be a briefer weathergrams issued Sun 13
June, then I'll mostly be unavailable until 19 June,

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 30 July 2010

2010-05-29T23:31:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 30 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

NORTH PACIFIC
TC AGATHA starts off the new North American Cyclone season, rolling into
Guatemala from the Pacific Ocean and its rain is turning ash from a
recent volcanic eruption to some sort of ready mix concrete.
GALAPAGOS TO MARQUESAS
Not much change from last week... Take off to just north of the equator
at first, and go to around 125W, and enjoy a following current and a
moderate wind from south or southeast. Then head direct for your
destination and winds should oblige at southeast 15 knots.
TROPICS
South Pacific Convergence zone SPCZ, after having most of its energy
taken off into the mid-latitudes last week, is slowly reforming now
along 10S, from Papua New Guinea to east of Solomons to Tuvalu/Tokelau
and extending to Samoa at times.
A combination of clouds from the tropics + jetstream intensification + a
large upper low feeding mid-latitude fronts resulted in a lot of
thunderstorms between Fiji and New Zealand last week, no doubt harassing
the Auckland to Fiji race fleet.
This week a trough is likely to form over Vanuatu on Thu/Fri 3/4 June
and deepen into a low to east of New Caledonia on Sun 6 June. The Low
should then get caught in a jetstream and shoot southeast and deepen
rapidly as it crosses the Kermadecs on Mon 7 June - avoid it then.
SUBTROPICAL RIDGE: STR
The High currently crossing southern NZ should wander along 40/45S
eastwards and get south of French Polynesia mid next week around 10
June. There is a rather mediocre zone of enhanced trade winds on its
northern side.
Next high to wander along the STR should also take the 40S latitude but
is likely to extend eastwards as a tongue rather than as a closed
centre... reaching Bass Strait from Tue 1 June to Thu 3 June and Central
NZ from Friday 4 to Saturday 5 June, just in time for start of NZ
Queen's Birthday holiday weekend.

TASMAN/NZ
Between the Highs mentioned above come the lows. Last week's lows took
their time to cross NZ, so that we had an opening gambit of strong NE
winds and rain last Monday, then a middle game as the rain band
spiralling into the centre stalled over South Island, and finally a
squash zone/eggbeater moulded by the low and the incoming High.

The next low has deepened off Sydney on schedule as picked in last
week's weathergram, but isn't as well positioned as last week's low to
develop much further. It will however take its time as it crosses NZ
and split into a multi-centred system on Tues 1 June.

For those waiting in Northland to sail off north, the useful SW winds
should arrive there on Thu 3 June. There may be another front crossing
Northland on Fri 4-Sat 5 June with a change to southerly/southeast
winds. Sun 6 June could be light winds at Northland, and then there
may be Ok winds for sailing north again on Mon/Tue 7/8 June. Enjoy.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM issued 23 May 2010

2010-05-22T23:11:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 23 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 125W,
and enjoy a following current and a moderate wind from south or
southeast. Then head direct for your destination and winds should
oblige and be southeast 15 knots. may be some tropical shower activity
around Marquesas this week.

TROPICS
South Pacific Convergence zone SPCZ was very active across Vanuatu/New
Caledonia to South of Fiji/Tonga last few days. A burst of convection
has been captured by northwest winds aloft and is wandering across
Vanuatu today (Sunday) and should then wander to the southeast, getting
to 998 very close to the Kermadecs on Tuesday morning and then fading
and heading south. This is the low that we were picking for the
Auckland to Fiji Yacht race would be at 981 near North Cape on Monday
night and would bring 8 metre + swells to near 30S on Tuesday - under
this new path the swells in that region then will be more like 4 metres.

There is another branch of the SPCZ stretching from Wallis/Futuna to
Tuvalu to Tokelau. This branch is expected to wander southwards across
Fiji on Monday and then across Tonga on Tuesday and Wednesday. Later in
the week a new SPCZ should reform over Papua New Guinea and Solomons.

SUBTROPICAL RIDGE: STR
High 1 has its cell east of New Zealand (we enjoyed it here on
Saturday), and is on its way to the east and should reach French
Polynesia longitudes on Thu/Fri 27/28 UTC with a squash zone of enhanced
trade winds on its northern side.

The STR is weak after that high, as the Tasman Sea turns into a low
breeding ground. High2, a cell east of Tasmania is all that is left in
our part of the STR and it will be forced to wait, and finally squeeze
across to south of NZ on Thu 27 May. For those waiting for the STR to
reassert itself across the Tasman Sea so that they can have a
comfortable voyage from Auckland to the tropics--- indications are, at
this stage, that you may need to wait til early June. I think the STR
tends to fade like this whenever there is a kerfuffle in the Sea Surface
Temperatures around Galapagos.
.

TASMAN/NZ
When the STR is weak the Tasman Sea becomes a low breeding ground. Last
Thursday night's low got to 999 near North Cape.

Low 1 for this week is 1005 in mid Tasman today and should drop to 985
as it crosses Cook Strait on Tuesday/Wed 25/26 May. At its peak on
Wednesday when centred east of Marlborough, there will be squally
westerlies and heavy swell over western NI, but of more importance will
be the squash zone between Low 1 and High 2 (referred to above). This
flow will drive SE winds directly onto the eastern SI, mixing cold and
moisture in a chamber of lowering pressure: a formula good for mountain
snow on the eastern slopes of our Alps.

Low 2 for this week should roll across New South Wales on Tue, be around
1005 near Lord Howe on Wed 26 May, 1001 near Norfolk on Thu 27 May and
1005 near North Cape on Friday 28 May. The squash zone between Low 2
and High2 should bring a large zone of easterly gales onto the eastern
NI during the 29/30 May weekend. This combination will make for a
larger impact that last Thursday's 999 low near North Cape. Avoid.

Low 3 should deepen offshore Sydney on Sat 29 May, making for a real
southerly buster: avoid.

I made a late night typo last week, so here's a correction: Those of
you who have email at sea can download the latest NZ high seas forecast
by sending an email to query@saildocs.com, no subject needed, with
message SEND http://bit.ly/subtropic, as well as listening to it on
ZLM.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 16 May 2010

2010-05-16T01:57:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 16 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 124W,
and enjoy a following current and a light southerly wind. Then head
direct for your destination and winds should obliging increase to 15
knots from the southeast or east. Weather mostly settled; some showers
around 92W and 100W. Also very showery along the Intertropical
convergence zone between 5 and 9N so don't stray that far away.

TROPICS
South Pacific Convergence zone SPCZ has been knocked around lately and
that zone of cloud and squalls stretching from off Queensland to south
of Fiji and then out to the southeast is a reflection of the subtropical
jet rather than the SPCZ.

The SPCZ is slowly reactivating around the Solomons to Tuvalu and around
Northern Cooks to French Polynesia. There is a burst of active
convection over Indonesia at present but that will take weeks to get
into the Pacific and is more likely to affect Micronesia rather than
South Pacific.

However, we should remember that squalls in that trough line south of
Fiji can still be a problem. I had an email today recording a good 35
knots of winds around 160 miles south of Suva. So keep in mind that
the GRIB files and isobars don't work 100% near troughs.

SUBTROPICAL RIDGE: STR
HIGH1 from last week continues to dominate proceedings and is 1038 at
40S 150W... should continue to wander east reaching 090W next weekend
with a touch to north to 33S where it will become the Andes High for a
while. As mentioned last week, there is a strong squash zone of the
northern side of High1--- many yachts were sheltering from it in Minerva
all last week. This squash zone is exacerbated between High 1 and a low
that has formed to southeast of French Polynesia - Fiji Met have just
issued a gale warning on this zone. The Low is blocked and is likely to
move south then southwest and fade into the next incoming trough of Tue
18 May.

Next High along the STR is barely showing itself as it crosses New
Caledonia tonight 16 May, and south of Fiji and Tonga on Tue/Wed 18 /
19 May and then should be more noticeable south of Southern cooks at
30S by 20 to 21 May.

Following High in the STR will be more to the South, rolling along 45S
to south of Tasmania on 20 May, heralded by a southerly outbreak that
may toss cold southerlies with rain then snow onto southern New Zealand
from Fri 20 to Sun 22 May.

TASMAN/NZ
Large Catherine-wheel low in the Tasman Sea is rotating clockwise
underneath its cut-off upper low and should finally cross NZ on Tue 18
May and its associated trough should reach Northland on Wed 19 May
followed by only brief SW winds.

Next trough rolls in from the southern ocean onto South Island from Fri
20 to sun 22 May, pushed in by that high in the STR, as mentioned above.

The Jet stream over Queensland looks primed to produce another Tasman
Low. Latest GFS model has this crossing the Tasman and reaching NZ
around 26 -27 May, but the latest EC model http://biy.ly/ecoz has its
warm fronts reaching NZ around 23 to 24 May, and that seems closer to
the observed recent rhythm in the STR. Those preparing for the Auckland
to Fiji race taking off on Sat 22 May will be keeping a close eye on
these models, and the http://bit.ly/7daywx model all during the coming
week.

Those of you who have email at sea can download the latest NZ high seas
forecast by sending an email to query@saildocs.com, no subject needed,
with message SEND http://bit.ly/suntropic, as well as listening to it
on ZLM.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 9 May 2010

2010-05-09T00:00:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 9 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 110W,
and enjoy a following current and a light southerly wind. 110W marks
an area of squally showers this week. After 110W head direct for
Marquesas (Nuku Hiva or Hiva Oa) and winds should obliging increase to
15 to 20 knots from the southeast, with settled weather.

TROPICS
South Pacific Convergence zone SPCZ is starting to reactivate this week
after a quiet time. It stretches across Papua New Guinea and Solomons to
northern Vanuatu, and this branch is expected to stretch to be across
Fiji and Tonga on Tue/Wed 11/12 May There is another branch from east
of Samoa to Southern Cooks, and this is likely to take a rare wandering
onto French Polynesia on Thu/Fri 13/14 May.

SUBTROPICAL RIDGE: STR
HIGH1 that moved east of New South Wales over the weekend is being
shunted over central New Zealand on Mon 9 May and should wander steadily
eastwards along 40S to east of NZ for the remainder of the week, with a
squash zone of enhanced trade winds on its northern side that should
affect southern Cooks from Wed 12 to Sun 16 may.

Then the STR goes through a weak period. The next High is expected to
wander across the eastern Australian Coast line on Sat/Sun 15/16 May,
just in time to kill the wind for Ella's Pink Lady as she arrives in
Sydney.

A small wedge of this ridge may get east along 22-23S to New Caledonia
and south of Fiji on 15/16 May and that will be preceded over New
Caledonia and Fiji by a period of light southerlies and clearing weather
on 12-14 May

TASMAN/NZ
Weather window for comfortable sailing out from Northland is closed this
week.

Low1 to northwest of Northland has to wait for High1 referred to above
to get east. So it's doing a loop tonight/ Monday and should then
travel south along 170E on Tue/Wed 11/12 May, fading as it crosses
Southland.

Around this time a large trough is expected to cross Tasmania, followed
by a very cold southerly that will be originating from the Antarctic ice
shelf- a polar outbreak. This trough should form a new low in mid
Tasman Sea on Thurs 13 May, and this low should cross central NZ on 14
to 16 May, with that polar outbreak fading as it arrives over the
southern South Island on Fri 14 May.

When a Low deepens like this in the Tasman Sea as it approaches central
New Zealand, it is able to draw in moist warm air and cool it with fresh
cold air: this is a well-known scenario for rain in NZ, so take time
out to clear those gutters of autumn leaves in readiness.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 3 May 2010

2010-05-02T01:14:00.000-07:00

WEATHERGRAM
YOTREPS
Issued 3 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

GALAPAGOS TO MARQUESAS
There is a build up of cloud around Galapagos at present, so maybe wait
a few days before departing if you like. Take off to just north of the
equator at first, and go to around 110W, and enjoy a following current
and light southerly winds. Do not go any further north than around 30
minutes north... After 110W head direct for Nuku Hiva, the entry port
for Marquesas, and winds should obliging increase to 15 to 20 knots from
the southeast, with settled weather.

TROPICS
South Pacific Convergence zone SPCZ is having a quiet time at present,
so enjoy this while it lasts... It is slowly reorganising across the
north end of the coral sea and then in a zone from Tuvalu to Southern
Cooks, but at present reasonably clear over Samoa. Should continue to
build and hold position this week, and may spread south towards Fiji
some stage next week 10-14 May.

A LOW is expected to form at the mid-latitude end of the SPCZ to south
of Southern cooks around 6-9 May and peel off to the southeast.

SUBTROPICAL RIDGE: STR
HIGH in Tasman Sea is expected to fade near western North Island and
then be reinforced by another HIGH on Monday 3 May. New combo High
should cross the central NZ area 4-5 May and then wander off to east of
North Island on 6-7 May . There will be a squash zone of enhance trade
winds on the north side of this High mainly along about 23 South from
around Niue to New Caledonia.

Following this High there should be a trough T1 that will cross NZ on
Fri/Sat 7-8 May. Then, from 8-12 May a HIGH is expected to migrate from
central Australia along 30S across northern Tasman sea. This will build
the STR and allow for some strong westerlies south of it over NZ next
week - a step towards winter in the south.

TASMAN/NZ
Not bad for heading off over next few days, but window closes by Thu 6
May.

Mediocre cold front on Monday 3 May, High on 4-5 May, then comes that
trough T1 referred to above.
Preceded by strong northerlies on Thu 6 May and followed by disturbed
westerlies from Sat 8 May.

Some models make more of this tough than others , occasionally hinting
at chance of a low between New Caledonia and Northland early next week.
This is an unsure scenario at present, and if it impacts on your
venture then do the double-check.

TASMANIA / NEW SOUTH WALES COAST
ELLA'S PINK LADY is now on last leg of a circumnavigation, with a
solo-sailor (still under 17). For her there's one more challenge, as
that trough T1 referred to above (due to cross NZ 6-8May) crosses
Tasmania and New South Wales on Tue-Wed 4-5 may. When the trough
interacts with the east Australian current this may generate some lows,
and these will peel off to South-southeast into the southern Ocean, but
one of them may deepen rapidly east of Tasmania on Wed 5 and generate a
large zone of gales, typical of any classic Sydney-Hobart. Then that
HIGH mentioned above should kill all the wind near Sydney on the 8-9
Weekend.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 25 April 2010

2010-04-25T01:10:00.001-07:00

WEATHERGRAM
YOTREPS
Issued 24 April 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 110W,
and enjoy a following current and light southerly winds. Do not go any
further north than around 30 minutes north... After 110W head direct for
Nuku Hiva, the entry port for Marquesas, and winds should obliging
increase to 15 to 20 knots from the southeast, with settled weather.

TROPICS
Tropical Cyclone SEAN formed over the seas northwest of Australia in the
past few days, and I'm thinking it is likely to be the last of the
season, so sailors can now start to heed those tropical sirens.

South Pacific Convergence zone SPCZ has been active from Coral Sea
eastwards across New Caledonia / southern Vanuatu to Fiji to Tonga to
Southern Cooks. There has been some surface flooding around Fiji and
Tonga, and there is a burst of convection over Fiji tonight as a Low
forms in the SPCZ trough. - This LOW is expected to move southeast over
the Lau group on Monday 26 April then slowly east along the SPCZ between
20 and 23S and be south of the Southern Cooks next weekend 1-2 May.

SUBTROPICAL RIDGE: STR
HIGH cell east of New Zealand is stalled until Tuesday and will then be
reinforced and move east along 35 to 40 South to be well south of French
Polynesia for the 1-2 May weekend. There is a squash zone of enhanced
trade winds on the north side of this system around about 25S, just
south of the SPCZ. Avoid.

Next HIGH in the STR is expected to cross inland Australia rather than
the Aussie Bight. The longer nights are helping make colder denser air
over inland Australia and this high is likely to move from South
Australia on Tuesday 27 April to New South Wales on the 1-2 May weekend
to northern North Island on 4-5 May. This High will push trade winds
into the Coral Sea knocking the SPCZ to Solomon Islands / Tuvalu.

TASMAN/NZ
Low in Tasman Sea should intensify as it wanders off to the south on Mon
26 April. Associated front should reach the North Island by Tuesday and
stall between Northland and East Coast from then til Thursday bringing
some welcome rain.

Usually around this time of year there is a cold SW change that whooshes
across NZ and makes cruising sailors shiver, up-anchor and head for
warmer climes. This is similar to a front that swoops across California
in October, called the Californian flush. Well, it isn't expect to be
very dramatic, but a deep Southern Ocean Low is expected to pass
eastwards to south of Tasmania on 27-28 April and south of NZ on 29-30
April and its associated front should bring a chilly SW/S change to the
South Island on Friday 30 April and North Island on Sat 1 May. So it
should be OK to depart NZ on 2 May.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com