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

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

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