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

13 May 2012

BOBGRAM issued 13 May 2012

WEATHERGRAM
YOTREPS
Issued 13 May 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.

The Southern Oscillation Index or SOI has bounced back into positive territory over the past week. Its 30 day running mean was mainly -0.6 in April, and started May at -1.1 but is plus 0.5 on 13 May. It is erratic.

Indian Monsoon seems to be arriving a few weeks ahead of schedule. See http://apdrc.soest.hawaii.edu/projects/monsoon/realtime-monidx.html .
It is too windy at present for those seeking the Himalayan Climbing window.

South Pacific Convergence Zone SPCZ has become quieter during last week, but is reasonably active across the Coral Sea, northern Vanuatu and Rotuma. It isn't expected to do much during the coming week.

Galapagos to Marquesas: A continuation of last week, all clear of squally showers now. Depart quickly SSW from Galapagos until 3S then WSW to 5S then west to 125W then direct.

SUBTROPICAL RIDGE STR
The STR is weakening around the date line as a large LOW from the southern Ocean expands its circulation northwards to around 25S. The old HIGH eats of NZ should move slowly east along 30S.

A new HIGH from the Aussie Bight is expected to cross New South Wales on Wed /Thu 17/18 May and move into the Tasman Sea on Friday 18 May. It will likely track along 30S, to north of NZ, by Mon 21 May.

NZ /Tasman Sea troughs
A LOW moved out and northeast-wards past Tasmania and into the Tasman Sea during this weekend. It is still expanding northwards and its associated front and disturbed westerly gales are likely to reach as far north as 30S. The SW winds on its western side are likely to draw air from 55S to NZ on Tuesday and Wednesday and then the Low may bottom out below 970hPa on Friday near 50S 160W—try and avoid this beast.

Departing from NZ for the tropics.
The SW flow over Northland should start easing on Wed 16 May; at this stage, things are looking good for those departing Thursday 17

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

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