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

24 January 2009

BOBGRAM7 issued 25 Jan 2009

WEATHERGRAM
YOTREPS
Issued 25 JAN 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.

We are now entering HIGH SUMMER... the southern hemisphere equivalent of
"the Dog Days' of a dawning Sirius that is associated with the hottest
time of the year. This year in Fiji, the return of the sun after two
drenching weeks has caused very humid conditions there indeed. NZ has a
superb example of a summer HIGH stalled over the North Island-- and thus
a westerly flow over the South Island --- all set to make this to be
likely to be the warmest week of the year for NZ.

TROPICS
The South Pacific Convergence Zone SPCZ is active in a zone from Tuvalu
to Samoa along with some westerly winds on its northern side. It has
dumped a lot of rain in a branch from Samoa to Southern Cooks over past
week, associated with a tropical depression. There was another wet
branch from Samoa to French Polynesia, and a weaker branch from Northern
Australia across the Coral Sea to Loyalty Islands.

Over Monday and Tuesday, there is a good chance that a low may form over
SPCZ and drift south over or just east of Tonga, fading back into a
trough from Wednesday 28 Jan. The main rain with this feature will be
on its eastern side as it travels south-it may well wander a bit to east
or west as well, so treat with respect.

Another Low may possibly form on SPCZ to North of Fiji - perhaps around
Rotuma - on or around Wed 28 Jan and then take a generally southwest
track across Vanuatu and onto New Caledonia around 2 Feb. Not sure on
this ... NOGAPS model seems to be overdoing these lows and EC model is
perhaps undergoing them for a change, so this is an amalgam of possible
proceedings. Next week/early in Feb I think (along with the EC model)
that the focus of the tropical lows will be the Coral Sea.

We are nearing the end of January and haven't had a cyclone named in the
South Pacific so far this season, but one of the lows mentioned in past
paragraph may become worthy enough.


SUBTROPICAL RIDGE
The HIGH stalled in the Tasman Sea / North Island area has already been
mentioned. There will be a High replacement on Tuesday (old high fades,
new High builds in South Tasman Sea behind a front that brings a cooling
and damp southerly change that will be welcomed by eastern NZ). The
New HIGH should be a BFH, a big fat high, building to 1030 hPa in
central Tasman Sea on Thursday and lasting there until another High
replacement occurs around Sat 31 Jan /Sun 1Feb.

There will be a well-defined squash zone of enhanced trade winds between
this Tasman HIGH and the low pressures in the Coral Sea. This squash
zone is expected to be strongest between New Caledonia and the
Queensland coast between 20 and 25S from Wednesday to Friday.

TASMAN SEA/NZ
The superb summer High scenario may well make this the sunniest and
warmest week of the year for much of the country (but several wet days
in Fiordland, and some isolated afternoon downpours where sea breezes
collide over hot hinterland along with the arrival of some cooler air
aloft as surface pressure drops.

Tuesday is the odd day out, with a cool damp southerly change affecting
east coast, probably reaching Canterbury near noon. SO, overall, it is
a welcoming week.


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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