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

17 May 2009

BOBGRAM7 issued 17 May 2009

WEATHERGRAM
YOTREPS
Issued 17 MAY 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
The South Pacific Convergence Zone SPCZ has been more active than normal
last week, stretching across the Solomons to Rotuma/Samoa and then
southeast roughly thru 20S 160W. It is expected to wander north and
south around that average position during the next week or two.

All looks normal on the Galapagos to Marquesas route.


SUBTROPICS
To east of 180 there is a subtropical HIGH near 40S 140W, somewhat
quasi-stationary, but it should be knocked more to 45S by the end of
this week, and extends out to 35S 100w.

This BIG FAT HIGH is maintaining two subtropical lows near 33to 35S at
present, one near 160 W (and this is killing the trade winds over
southern Cooks and French Polynesia, and t'other near 125W, these are
moving east or east southeast. Avoid their squash zones.

The subtropical ridge is very weak at present between 160E and 160W,
with troughs over NZ. Cold air has got into the subtropics and spun up
a small subtropical Low to east of New Caledonia today; this is the
"complication" mentioned in last weeks weathergram. It is expected to
cross the Kermadecs on Monday UTC and move off to the southeast. If you
are in the vicinity remember that it is easiest to clockwise around this
low.

The next BIG HIGH "upstream" is expected to move into the South Tasman
Sea on Thursday 21 May and then wander north into the northern Tasman
Sea over the weekend and early next week. As this High enters the south
Tasman Sea a Low is likely to form between Brisbane and Lord Howe Island
and then move east towards Kermadecs early next week. Avoid the squash
zone between Low and High--- looks like it'll bring big swells to Coffs
Harbour, peaking around Friday Saturday.
This Squash zone will extend eastwards along 33S reaching 180 by Fri 22
May--- anyone sailing northwards from Northland this week should try and
get north quick to beat this squash zone.

NZ AREA
Yes, It's been troughy. We've had heaps of rain over the Southern Alps
last week and the fronts have been thundery and proceeded by vigorous
northwest flows. One-more-of-these-fronts is likely on Monday and then
the flow should go more southerly thanks to rising pressures from the
incoming High.

These southerly winds may be snowy in the south on late Monday/Tuesday
and more so over eastern NZ on Wednesday (helped by a LOW that is likely
to deepen on Wed between Canterbury and Chathams. Later in the week
lighter winds and clearing skies should bring a dose of frosty dawns to
the South Island/central North Island.

Those waiting in Northland to sail off to the north should take off as
soon as the SW winds arrive around Tuesday. This is so as to try and
get north of 30S before the squash zone arrives--- then again, the
squash zone will mean hearty easterly winds and some will prefer that
perhaps.

From Friday 22 to Tuesday 26 May the squash zone between Low and High
will likely be over northern NZ-brace for it or be embarrassed.

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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