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

13 December 2008

BOBGRAM7 issued 14 Dec 2008

WEATHERGRAM
YOTREPS
Issued 14 Dec 2008
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
Near equatorial westerly winds are starting to appear in Timor Sea,
indicating a pulse of activity in the Inter Tropical Convergence Zone
ITCZ. EC model is keen to trigger a tropical cyclone out of this well
west of Darwin on 19 Dec taking it inland and killing it by 22 Dec.
Other models are not so sure, so chances at this stage are less than
50%. This pulse of activity is called a Madden Julian Oscillation MJO
and is likely to reach Coral Sea between Christmas and New Year
increasing chances then of development in our part of the world. Ah
well, most tropical sailors are ashore then.

South Pacific Convergence Zone SPCZ went south last week, and a small
development between Vanuatu and Fiji took much of the activity in the
SPCZ off to the SE. SPCZ is now lurking from Solomons to Tuvalu to
Wallis/Futuna/Samoa to between Niue and Southern Cooks. Forecast is for
SPCZ to drift south again late this week and for another small low or
trough to form (again) between Vanuatu and Fiji on 20 Dec and to move
southeast on 21/22Dec with a strengthening squash zone on its southern
side --- between the trough and a High over NZ.

Not much expected elsewhere in South Pacific tropics, mainly weak NE
winds on eastern side of SPCZ and weak variable winds to west and south
of SPCZ gradually becoming southeasterly.

SUBTROPICAL RIDGE
On 16 Dec a small High may bud off eastern Australia into Tasman Sea,
and then wander east along 30S until it fades away south of French
Polynesia on 21 Dec.

More intense High is likely to bud off eastern Australia/Tasmania into
Tasman Sea at 35S on 19 Dec, and cross NZ 21/22 Dec, and maybe reform a
new centre over Chatham Islands on 23 Dec, that might linger there 24-27
Dec. Happy Christmas Chatham Islanders!

TASMAN SEA/NZ
The remains of that large Low that moved off Australia over the weekend
are expected to weaken somewhat as they cross NZ on 15-16 Dec, followed
by cool SW flow on 17-18 Dec. New low is forecast to form on a front in
the Tasman Sea on 18 Dec and cross NZ of 19 Dec, followed by a S/SW flow
on 20 Dec.

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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