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

26 February 2012

BOBGRAM issued 26 Feb 2011

WEATHERGRAM
YOTREPS
Issued 26 Feb 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 continues to relax in the atmosphere. Average atmospheric SOI (30day running mean) was 0.58 on 20 Feb and -0.3 on 26 Feb, its first negative week since April 2010.

There is a zone of enhanced tropical convection stretching from Indian Ocean across Indonesia to North Australia and this is expected to reach Coral Sea between 10 and 15 March
. The South Pacific Convergence zone SPCZ has been weak for the past week and mainly concentrated between Tuvalu and Northern Tonga. During the coming week a small trough is expected to bud off the SPCZ over southern Tonga by Tuesday 28 Feb and then move off to the south, as the SPCZ slowly rebuilds over Coral Sea,

SUBTROPICAL RIDGE STR
High1 near 140W and south of French Polynesia is blocked and should stay put this week, causing features upstream to bunch up and stall.

High2 in North Tasman Sea is expected to go further north on Monday and the swing eastwards along 30S on Tuesday and Wednesday then merge with high 1 east of 180 on Thursday.


High3 currently in Aussie Bight is expected to cross south of Tasmania on Friday and into the South Tasman on Saturday its them and should cross Tasmania on Friday and then into South Tasman Sea on Saturday/Sunday/Monday 3/4/5 March,

TASMAN SEA/NZ AREA
FRONT is expected to move from Tasman Sea onto South Island on Tuesday 28 Feb, A LOW should deepen on this front to east of the South Island on Wed/Thu 29 Feb/1 Mar producing 2 days of S or SW flow over NZ. This Low should move away on Friday 2 Mar and thus produce light winds over NZ but an EASTERLY flow over southern South Island.

A new LOW should form near Lord Howe Island on Thu 1 Mar and deepen as it moves onto the Auckland area on Sat 3 March with a strong S or SE flow over NZ. Avoid,

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

20 February 2012

BOBGRAM issued 20 Feb 2012 sent 21 Feb

WEATHERGRAM
YOTREPS
Issued 20 Feb 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 continues to relax in the atmosphere. Average atmospheric SOI (30day running mean) was 1.07 on 11th Feb and 0.58 on 20 Feb.

There is a zone of enhanced tropical convection stretching from Indian ocean (TC GIOVANA near Madagascar is part of this) across Indonesia to Philippines. There is a counterbalancing zone of suppressed convection now over much of the Pacific Ocean. The South Pacific Convergence zone SPCZ has weakened and become disjoint since last week and is roughly from PNG to Vanuatu and across Tuvalu and Tokelau, with another branch around French Polynesia. It isn't expected to do anything significant this week. However a LOW should form on the SE end of the SPCZ to south of southern Cooks by Tues 21 Feb and wander off to the SE, stealing away the trade winds in that part of the tropics. Trade winds are likely all week from Niue to Queensland and should return to Southern Cooks from Wed 22 Feb.

The GFS models picking that SPCZ may reactivated over Vanuatu/Fiji on weekend of 25/26 Feb, but EC model is not so keen and I'll go with the EC on this.

SUBTROPICAL RIDGE STR
High that moved off to east of NZ over the weekend is expected to wander east along 42S until Wed 23 Feb and then go north and fade as a new lobe reforms at 45S. This part of the STR looks healthy and is supporting some good trade winds in the tropics for good 'Island hopping' over the next week or so,

Next STR is in Aussie Bight and is expected to spread into northern Tasman Sea by Saturday 25 Feb. It should then extend across the South Island by Sun 26 Feb, making a cool S/SE flow for eastern NZ.

TASMAN SEA/NZ AREA
Low that formed crossing the EAC (east Australian current) today is expected to be well supported aloft for development as it follows the trough that i9s set for it across the South Island: 1000 near Westland on Thu, 990 to SE of Otago on Friday and 960 near 58S on Saturday. Technical name for a low that deepens 24hPa or more in 24hr is a 'meteorological bomb'.
The southerly flow reaching NZ east coast on Sat 25 Feb as that low goes away and the next STR crosses the Tasman Sea is expected to come from 55S. A cool change.

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

BOBGRAM issued 20 Feb 2012

WEATHERGRAM

YOTREPS

Issued 20 Feb 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 continues to relax in the atmosphere.  Average atmospheric SOI (30day running mean) was 1.07 on 11th Feb and 0.58 on 20 Feb.

 

There is a zone of enhanced tropical convection stretching from Indian ocean (TC GIOVANA near Madagascar is part of this) across Indonesia to Philippines.  There is a counterbalancing zone of suppressed convection now over much of the Pacific Ocean. The South Pacific Convergence zone SPCZ has weakened and become disjoint since last week and is roughly from PNG to Vanuatu and across Tuvalu and Tokelau, with another branch around French Polynesia. It isn’t expected to do anything significant this week. However a LOW should form on the SZE end of the SPC Z to south of southern Cooks by Tue 21 Feb and wander off to the SE, stealing away the trade winds in that part of the tropics.  Trade winds are likely all week from Niue to Queensland and should return to Southern Cooks from Wed 22 Feb.

 

The GFS models picking that SPCZ may reactivated over Vanuatu/Fiji on weekend of 25/26 Feb, but EC model is not so keen and I’ll go with the EC on this.

 

SUBTROPICAL RIDGE STR

High that moved off to east of NZ over the weekend is expected to wander east along 42S until Wed 23 Feb and then go north and fade as a new lobe reforms at 45S.  This part of the STR looks healthy and is supporting some good trade winds in the tropics for good ‘Island hopping’ over the next week or so,

 

Next STR is in Aussie Bight and is expected to spread into northern Tasman Sea by Saturday 25 Feb. It should then extend across the South Island by Sun 26 Feb, making a cool S/SE flow for eastern NZ.

 

TASMAN SEA/NZ AREA

Low that formed crossing the EAC (east Australian current) today is expected to be well supported aloft for development as it follows the trough that i9s set for it across the South Island: 1000 near Westland on Thu, 990 to SE of Otago on Friday and 960 near 58S on Saturday. Technical name for a low that deepens 24hPa or more in 24hr is a ‘meteorological bomb’.

The southerly flow reaching NZ east coast on Sat 25 Feb as that low goes away and the next STR crosses the Tasman Sea is expected to come from 55S.  A cool change.

 

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

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

Feedback: bobmcd@xtra.co.nz, work: bobmcdavitt@hotmail.com

 

 

12 February 2012

BOBGRAM issued 12 Feb 2012

WEATHERGRAM
YOTREPS
Issued 12 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 indicator in the atmosphere, the Southern Oscillation Index, is hovering around 1 (moderate). It was 0.79 on 5th February and 1.07 on 11th Feb.

The MJO cycle of enhanced convection peaked over the past fortnight and is now relaxing. At its peak TC CYRIL formed and moved off toe the southeast of Tonga. TC JASMINE formed in the Coral Sea and managed to skirt around the Loyalty Islands then south and southeast to be now near and SW of Minerva. It has managed to cocoon its own blob of tropical air to work with, even though it is now in sea surface temperatures not quite warm enough to continue it. So it is weakening, but will take a while yet to spin down. It is expected to be deflected north back into the tropics, to west of Tongatapu by Wednesday and then to weaken and go southeast. Avoid Minerva.

The South Pacific Convergence zone SPCZ remains active from Papua New Guinea to Solomons to Fiji/Tonga then to the southeast. The moisture of TC JASMINE has broken away from the SPCZ and is doing its own thing. A low is expected to form on the SPCZ to SW of Southern Cooks on Monday and then move off to the southeast Another Low is likely to form in the Coral Sea on Mon 20 Feb but is expected to move off to the SE too quickly to deepen any further. The next MJO cycle (and enhanced risk of cyclone formation) is now expected to be mid-to-late March. HOWEVER, Tropical cyclones may form between MJO episodes so take care if planning a tropical dash.

SUBTROPICAL RIDGE STR
A weak STR is in the Tasman Sea today and exerting a ridge across southern South Island towards Chathams. This STR is likely to be disrupted by a trough over next few days… one lobe may reform over Chathams on Mon 13 Feb and move off to the east --- so that there may be a squash zone between it and the remains of JASMINE. The lobe left behind in the mid Tasman Sea may finally reach North Island on Sat 18 Feb.

TASMAN SEA/NZ AREA
That low in the mid Tasman Sea today 12 Feb is disruptive. It has with it the moisture that has been flooding parts of the Australian east coast over the past week. However these clouds are now coming up against a block--- this will slow their motion and as they will drift away from the support of their rising motion the result is likely to be a rather chaotic mixture of patchy rain over NZ on Tue-wed-Thu-Fri 14-15-16-17 Feb. As the low weakens winds around it should slacken, and become no good for sailing but good for motoring for anyone planning a trans-Tasman trip.

Next trough is currently near mid-Aussie bight and should cross Tasmania on Thursday 16 Feb and South Island on Sat 18Feb (preceded by a strong NW flow over southern NZ on Fri 17). It then may stall over NZ into the following week.
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Note that I shall be retiring from MetService on Fri 17 Feb (60th birthday) and will be AWAY FROM email Sat/Sun/Mon—should be back on deck with another weathergram by Tue 21 Feb. Also I intend to continue with these weathergrams + with being available to provide weather information to cruising sailors into my retirement--- this is what I call my 'cruise mode'.
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The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback: bobmcd@xtra.co.nz, work: bobmcdavitt@hotmail.com

05 February 2012

BOBGRAM issued 5 Feb 2012

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

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