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

21 September 2008

BOBGRAM7 issued 21 Sep 2008

WEATHERGRAM
YOTREPS
Issued 21 Sep 2008 NZST
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 below are given in UTC unless otherwise stated.

The overhead sun crosses the equator at 1544Utc on Monday 22 Sep (around
4am Tuesday in NZ) - its about a day after the usual 21st sep because of
the leap day we had this year. Around the equinox we sometimes notice a
twinning of the ITCZ with the South Pacific Convergence Zone SPCZ, and a
branch of the SPCZ intensifies along 10South from about Tuvalu /Tokelau
to Northern Cooks and sometimes to Marquesas-no sign of this yet but it
may appear.

TROPICS Easterly winds to north and southeast winds to south of the
SPCZ. The winds are strong within the SPCZ over northern parts of Coral
Sea (avoid). And the SPCZ is active from there to North of Vanuatu to
Rotuma/Wallis/Futuna to Tonga to Niue. It is expected to travel south
this week, reaching Vanuatu/Fiji on Mon/Tue then fading away on Wed/Thu.
In this southern excursion a small LOW may form in Coral Sea on Fri/Sat
then head south into Tasman Sea early next week bringing wet NE winds to
New Caledonia on Fri/Sat. There will be a squash zone on the south side
of this LOW so take care if travelling between Vanuatu/New Caledonia and
Australia.

SUBTROPICS
For those of you from the Northern Hemisphere-welcome to the South
pacific with its migratory HIGHS.

HIGH between Norfolk and Raoul on Sunday is moving slowly along 33S and
should fade east of 180 by Thu.

HIGH on Aussie Coast on Sun should travel along 35S reaching Tasman Sea
wed/Thu and Northland on Fri/Sat and tongue out a ridge along 33S to
south of French Polynesia early next week.

On the northern side of these HIGHs there will be an enhancement of the
trade winds--- mainly between 25 and 20S.


TASMAN/NZ
Between the HIGHS are troughs and fronts, but no LOWs this week. So it
is a typical spring pattern.

First front is fading over North Island Sun/Mon.

Second front should cross South Island on Tue, preceded by strong NW
flow (especially for eastern areas) and accompanied by heavy rain in
western areas. Then fade over North Island on Wed.

Third front should reach South Island on Friday and hang about the North
Island on Saturday and Sunday.

Try and plan your Northland arrival/departure dates to be on Tuesday
/Thursday -Friday; in-between days rather than frontal days.


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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