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

13 November 2011

BOBGRAM issued 13 Nov

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

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