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Bob McDavitt's ideas for sailing weather around the South pacific

24 November 2013

BOBGRAM issued 24/25 Nov 2013

WEATHERGRAM
YOTREPS
Issued 24 November 2013
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.

Thanks to the yacht people at Opua who came along on Friday and allowed me to share with them my ideas, and for the feedback they gave me regarding my weather forecasting. Thanks also to those in Gulf Harbour who fed and watered me this Sunday evening. All appreciated.

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is the NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

TROPICAL TOPICS
The first cyclone for the southern hemisphere's new cyclone season is TC Alessia and is moving east inland near Darwin over next few days.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is in its northern most position at present and rather weak and disjointed, but it is expected to activate this week and drift slowly south onto Samoa by early December.

Sub-tropical Ridge STR
The STR is now oscillating between its southern latitude band and its northern latitude band. That High which is expected to be over Aussie Bight by Wednesday should move NE into the Tasman Sea by Sunday/Monday, bringing some settled weather to the Tasman Sea area after rather unsettled weather there this week.

Tasman Sea/NZ.
Front in the Tasman Sea is expected to cross the North Island on Wednesday bringing some welcome rain after a dry spell, and this is expected to be followed by a Low. Another weaker trough is expected to cross the North Island on Sunday 1 December, followed by settled weather of a High.

Briefings
Between tropics and NZ
Slack winds for starters this week—then a useful northerly flow from Monday to Wednesday, then a warm front on Wednesday/Thursday, then slack winds again—So weather pattern is not the best for getting from tropics to NZ this week, but if you don't mind doing some motoring and going through a warm front at some stage, then the voyage can be done.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

17 November 2013

BOBGRAM issued 17 Nov 2013

WEATHERGRAM
YOTREPS
Issued 17 November 2013
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.

SOI: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.
It reached a high of 0.52 on 22 September, and since then has dropped. On 17 November it has a 30-day running mean of -0.3, and is trending downwards.

TROPICAL TOPICS
Things seem to have gone quiet at present – no tropical cyclones today.
An interesting comparison of the geographical extent of TC HIAYAN with that of TC KATRINA can be seen at http://lnk.ie/KWJT/e=bobmcd1.bobgram@blogger.com/http://tropic.ssec.wisc.edu/temp/Geographical-Coverage-Hiayan-vs-Katrina.jpg

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ has retreated to it more northern position in the past week and is now expected to go through a quiet period for the next week or more.
A Low is expected to form in a trough that is crossing New Caledonia on Monday. This Low should then deepen between Fiji and NZ on Tuesday and Wednesday. On Thursday its associated trough should cross Fiji and on Friday it should cross Tonga. Following this trough there may be a few days of light variable winds over New Caledonia until Friday and over Fiji until Saturday and Tonga until Sunday 24 November.

Sub-tropical Ridge STR
The STR went to the southern limit if its travel last week and is expected to stay well south of normal this week. This is a pattern sometimes called 'low index' and gives plenty of room for lows to form and expand between the SPCZ and the STR. This is exactly what is expected to happen this week with a low deepening between Fiji and NZ.

Tasman Sea/NZ.
High over the South Island is expected to travel off the east on Monday/Tuesday maintaining a NE flow over NZ. Low between NZ and Fiji should reach peak intensity near 28-29S 175-179E on Wednesday and then weaken as it moves off to the southeast.
Trough in the south Tasman Sea is expected to cross the South Island on Thursday and then fade away as it travels off to the east in Friday. This is likely to be followed by light winds for a few days.

Briefings
Between tropics and NZ
The Low between Fiji and New Zealand and the trough and light winds that follow it basically closes down the idea of getting a cruisey sail to NZ this week. Some may want to get going in the light winds that follow, but others will prefer to wait for some steady and useful breezes to return – maybe this weekend or early next week.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

10 November 2013

BOBGRAM issued 10 Nov 2013

WEATHERGRAM
YOTREPS
Issued 10 November 2013

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.

XTRA are disabling my bobmcd@xtra.co.nz account every time I send a weathergram blog now. Very inconvenient so I think I'll change the sending address to bob@metbob.com slowly over the next few weeks. Those who have bobmcd@xtra.co.nz white listed on their sailmail or winlink accounts (on list of allowable emails):- please also white list bob@metbob.com , thanks- easiest way to do this is to send an email from your account to bob@metbob.com .

SST: The Sea Surface temperature anomaly is a good indicator as to where the weather may behave 'normally' or 'abnormally'. The latest anomaly map over the South Pacific shows an inter-lace of cool and warm areas along the equator between the dateline and Peru. This is the zone that triggers an El Nino or a La Nina but it isn't quite doing either at present.

There is a zone of 'warmer than normal' covering the region from Solomons across Fiji to Tonga. This might help tropical cyclones to form or offer them a track to follow. Too early to tell, but keep this in mind.

TROPICAL TOPICS
TC HAIYAN was heralded as the world's strongest typhoon of the year before it made landfall in the Philippines, and now the death toll from this storm is estimated to be over 10,000 with over 4 million people being affected by this one day event. It is now losing intensity and turning north and should fade over south China in the next few days.

(Add a couple of 'r's, and then 'Terror' is a meteorologist's middle name.)

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is slowly getting more active and stretches from Solomons to Wallis/Futuna/Samoa to southern French Polynesia, with a few side branch convergence zones CZ. A Low is expected to form in the CZ crossing Southern Cooks this weekend producing a squash zone of reinforced easterly winds near 30S from 140 to 160W early next week.

Sub-tropical Ridge STR
After last week's steady progression of highs and Lows in the mid-latitudes, the STR spent last week travelling south, and is now in its southern setting. This is a pattern sometimes called 'low index' and is expected to continue this week as well, with plenty of room for lows to form between the SPCZ and the STR.

Tasman Sea/NZ.
A Low is now expected to form within the heat trough over Australia and move across 30S on Sunday 17th and deepen near Lord Howe Island early next week. A front associated with its trough is expected to reach New Caledonia by Monday 18 Nov and maybe Northland by Wednesday 20th November, preceded by strong NE winds. Avoid.

Route Briefings
Between tropics and NZ
Try and time your voyage from the tropics so the arrival tine in New Zealand does NOT coincide with a front or strong winds.
The current pattern looks promising- High pressure over NZ from now until Monday 18th Nov are expected to maintain much the same pattern with a flow that is SE/E flow over New Caledonia /Fiji/Tonga and a weaker NE to Opua. Good for departures on Monday and Tuesday.

However it is not expected to last this way for long.
A LOW is expected to move from central Australia to the Lord Howe area on or by Sunday 17 Nov, and may become slow-moving there next week. An associated FRONT is likely to reach New Caledonia by Monday 18 Nov and Northland by Wednesday 20 November. The NE winds ahead of this front may aid your voyage, but not if they get strong. Still too far away to tell exactly.

Since the sailing time for a boat capable of going up to 6 knots in the likely winds for this voyage from tropics to NZ is around 7 days to Opua, a departure on Tuesday 12th or early on 13th may get you to Opua before the front on the 20th, but a later departure may have an encounter with strong winds from that front. This is all still rather hazy, so ask for an update.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at metbob.com
Feedback to bob@metbob.com

03 November 2013

BOBGRAM issued 3 Nov 2013

WEATHERGRAM
YOTREPS
Issued 3 November 2013

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.

Another quick Weathergram this week.

Last week XTRA changed their email server settings and only allowed bobmcd@xtra.co.nz to send 200 of these emails to my email list of 620. So I resent via bob@metbob.com but several of you do not have that address set on their white list of allowable emails, and would have missed out. I'm hoping tonight's edition gets to you all.

SOI: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.

It reached a high of 0.52 on 22 September, and since then has dropped to around zero. On 3 November it has a 30-day running mean of -0.16 , close to zero.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to spend most of this week north of 15S.

Sub-tropical Ridge STR
The STR has weakened to a few lines mainly along 25S. Between 25S and 45S the South Pacific this week has a near regular steady progression of Highs and Lows, all mainly travelling along 40S.

The Low which is expected over North Island on Wednesday should travel off to the southeast and weaken.

The next High from the west is expected to travel across Tasmania/South Tasman Sea on Mon 11 Nov. This High is then expected to intensify over or just east of NZ early to mid-next week, 12-15 November, and form a squash zone of strong easterly winds between NZ and Fiji /Tonga for a few days. Avoid.

Route Briefings
Between tropics and NZ

Try and time your voyage from the tropics so the arrival tine in New Zealand does NOT coincide with a front or strong winds.

The Low crossing the North Island during mid-week has OK winds in its trough between NZ and the tropics—except that some swell over 3 metres may get as far north as 25S on 6 November.

From 12 November onwards (mid next week) some strong easterly winds are likely between NZ and the tropics because of the squash zone of the north side of a large High. It's too far away to tell exactly at this stage, but this needs to be taken into account by anyone wishing to depart from the tropics late this week, heading for NZ.

See my yotpak at http://lnk.ie/KFRS/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Website is at http://lnk.ie/KFRT/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

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