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

19 February 2011

BOBGRAM7 issued 20 Feb 2011

WEATHERGRAM
YOTREPS
Issued 20 February 2011
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.

La NINA is still strong, but weakening. Average atmospheric SOI over 30
days to 19 Feb Jan is 1.9, steady in the past week after dropping 0.5 in
early Feb.

TROPICS
South Pacific Convergence Zone SPCZ spent last week mainly over a wide
altitude zone between 10 and 20 S from Vanuatu to Tonga, with several
regions of tropical downpour. ATU was named near Vanuatu on Saturday. In
Africa (Ghana), the word ATU is occasionally given to a boy born on a
Saturday, so this is seemingly appropriate -however, in Polynesia, ATU
is the Samoan mythical name for the first man to settle in Fiji. The
system is certainly hugging Vanuatu, looking at today's satellite
imagery, may be doing a loop as it slowly re-curves to the south.
Future track is most likely to be south and then southeast--- kicked
along by upper NW winds already in place at 20 to 25S.

ATU is likely to take with it a lot of the energy/activity that is in
the current SPCZ, so it will slowly rebuild after Wednesday along the
trough area that will stay behind over Fiji to Niue. May be OK for some
Island hopping in this hiatus period, but no steady winds.

TC DIANNE off Western Australia is going south and following the Leeuwin
current. It may clip some coastal areas in the process.

King Tides on Sun 20 to Tue 22 Feb, so give these cyclones a wide berth.


SUBTROPICAL RIDGE:
HIGH1 is wandering northeast from 45S 160W to 40S 140W this week, and
maintains a disturbed NE flow on its "back shoulder"(NW quadrant)
HIGH2 starts this week crossing the Aussie Bight and should cross
Tasmania on Friday and then travel northeast across Tasman Sea on Sat 26
Feb and central NZ on Sun 27 Feb.

NZ Area
Transitional trough between HIGH1 and HIGH2 to approach South Island on
Monday (heavy rain tonight in the SW) and cross NZ on Tuesday followed
by a southerly wind change on Wednesday. A challenge for the SIMRAD
Round North Island Fleet sailing counter clockwise from north end to
Wellington, restarting on Tuesday. This trough is expected to linger
off to east of North Island on Thursday as remains of ATU roll SE along
the trough line--- this may throw swells at North Island east coast and
perhaps some rain, but its main wind and rain are likely to be well off
to east. May sideswipe Chathams on Friday.

One more SW to southerly front on Friday, and then clearing weather on
Saturday as HIGH2 arrives. On Sun 27 Feb, there may be a NW flow over
Southland and an easterly surge over Northland/Auckland (just like Wed
16 Feb).


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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