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

29 January 2012

BOBGRAM issued 29 Jan 2012

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

22 January 2012

BOBGRAM issued 22 Jan 2012

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

14 January 2012

BOBGRAM issued 15 Jan 212

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

07 January 2012

BOBGRAM issued 8 Jan

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

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