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

09 August 2008

BOBGRAM7 issued 10 August 2008

WEATHERGRAM
YOTREPS
Issued 10 August 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(Disclaimer: Weather is a mix of pattern and chaos, these ideas come
from the patterned world of weather maps, so please fine-tune to your
place).

TROPICS
South Pacific Convergence Zone SPCZ continues to linger at the northern
end of its range, along 10 South latitude from Solomons to Tuvalu, and
should spring to life from Tokelau to northern parts of French Polynesia
later this week.
This means it is lingering near Suvarov, so those hopping west from
French Polynesia should go via Aitutaki or Niue rather than the Suvarov
way.

Some of its moisture occasionally branches off to the south and mixes
with the mid-latitude troughs as they travel from west to east.
One of these mid-latitude troughs visited New Caledonia and Fiji last
week, and another is likely to reach New Caledonia on Monday 11 August
UTC and brush past Fiji on Wed 13 Aug UTC. These troughs are reasonably
mediocre, but they do bring periods of variable wind.

SUBTROPICS
Between these troughs we have subtropical ridges/Highs, these were weak
over past few weeks but are becoming more noticeable now. They are
migrating from west to east mainly along 30 s. One is over North
Island/ Kermadecs today/Monday 11 Aug UTC and should be south of French
Polynesia on Thu 14 Aug, and the next is likely to blossom sat 30S south
of Southern Cools around Sat 16 Aug UTC. North of these highs there is
a zone of enhanced trade winds in the tropics especially around 20S.

SO, trade winds in the tropics this week go up and down in speed as
ridge and troughs pass by in the subtropics Otherwise it is likely to be
a weak of trade winds in the SW Pacific.

TASMAN/NZ AREA
T'was good to see the sun over NZ today from that passing ridge - first
in many weeks. But it was a cold High and didn't last long. The LOWS
are still deepening in the Tasman Sea, but they are not blocked like
they were in late July.

Next Low is already deepening near Sydney today 10 Aug and its fronts
are expected to cross NZ late 11 and on 12 Aug UTC with the LOW crossing
the South Island. This should be followed by a disturbed westerly flow,
with another front on Thu 14 Aug UTC and a LOW affecting southern parts
of Tasman Sea/NZ on 16-17 Aug followed by cold southerlies. Avoid
these fronts and lows. The westerly to southerly winds in the Tasman Sea
again this week will make it hard for anyone wanting to sail to Sydney.

The terms used here are more fully explained in the METSERVICE Yacht
Pack.
More info at http://weathergram.blogspot.com Feedback to
bob.mcdavitt@metservice.com

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