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

21 August 2011

BOBGRAM issued 21 Aug 2011

WEATHERGRAM
YOTREPS
Issued 21 August 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.

TROPICS
Southern Oscillation Index SOI is in the positive and relaxing this week: its 30day running mean was 0.87 on 12 August and 0.47 on 20 August. .

South Pacific Convergence Zone SPCZ is steady in the zone from Coral Sea to New Caledonia. This zone has been caught by a jetstream and is being wrapped into a small surface low that started off near the east Australia coast a few days ago. This system has a few more days to run, mainly between Lord Howe and Norfolk Island and then should move west towards the Queensland coast and fade. Avoid.

There is another convergence zone – strong to east of northern Vanuatu then weak and lying across Wallis and Futuna then southeast towards French Polynesia. This system is expected to remain slow-moving this week, and then is likely to activate early next week with a LOW forming between Southern Cooks and French Polynesia.

SUBTROPICAL RIDGE STR
STR had a few weak weeks in the South pacific and is about to go through a counter-balancing strong period. The BFH Big fat High in Tasman Sea is a slow-mover and should finally reach Northland on Sat/Sun 27/28 Aug and then next week move along 40S to east of NZ. There are enhanced trade winds in a squash zone in the tropics on north side of this high.

TASMAN SEA/NZ AREA
Westerly winds are expected to return to South island by Wed 24 Aug, warming up places east of the divide. A strong gusty NW flow should arrive over much of NZ during the Sat/Sun 27/28 weekend, and an active trough then may cross NZ on Mon/Tue 29/30 Aug.

SAILING TO/FROM NORTHERN NZ.
The squash zone in the tropics is only recommended for spirited sailors and is expected to start easing by end of the week. It is OK until Friday to depart from Northland to north or east, and Sat/Sun 27/28 Aug are looking good as target arrival dates for voyages to Northland.

Congratulations to Bruce Arms for wiping almost 3 days off the record for a solo circumnavigation of Australia. Way to go , bro!.

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

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