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

20 June 2009

BOBGRAM7 issued 21 June 2009 (winter solstice)

WEATHERGRAM
YOTREPS
Issued 21 June 2009
Bob McDavitt's ideas for sailing around the South Pacific.
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.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone SPCZ has recently been active in a
zone from northern Coral Sea to northern Vanuatu to Fiji - activity (not
quite the low mentioned in the last weathergram but wet enough to cause
flood warning in Fiji on Saturday) is now sliding over Wallis/Futuna
(Sunday UTC) and should slip SE and fade over Southern Cooks on Monday
UTC. This zone is now moving slowly NORTH and is likely to stall in a
zone from Solomons to Samoa from Thursday onwards.

The other weaker SPCZ zone has been between Tuvalu and Tokelau, and this
is expected to fade over ne few days.

The Galapagos to Marquesas route is all quiet now, but easterly winds to
Marquesas are less than normal and this trend may continue, yuck.

SUBTROPICAL RIDGE
A winter HIGH (caused by cold air) in the Tasman Sea is supported
strongly aloft by a planetary wave and a medium wave, so will be slow to
change this week. Its southern parts decay fastest and this causes an
apparent northeast displacement of the system across North Island on
Wednesday. Then there should be a steady eastwards movement of the HIGH
"sausage" along 30S.

Winter Highs bring frost and, as they fade, fog.

On the northern side of this is a squash zone of enhanced trade winds.
This currently stretches all the way from southern Tonga to Lord Howe
Island and should move east with the HIGH and be from French Polynesia
to Fiji on Sat 27 June. Avoid.

NZ and TASMAN SEA
In the western shoulder of the HIGH there will be a series of troughs
and Lows. First LOW is likely to form east of Tasmania on Tuesday with
a trough crossing Lord Howe on Wednesday, and weaken over NZ on Friday.
A new low is likely to form between Lord Howe and New Caledonia on
Friday /Saturday and MAY deepen quickly as it moves towards central NZ
on Sunday and Monday, making for a strong wet NE flow over Northland
this weekend for that start of the NOUMEA 2009 yacht race. And then
another trough is likely to cross New Caledonia on Monday/Tuesday 29/30
June. All worth avoiding.


The terms used 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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