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

08 March 2009

BOBGRAM7 issued 8 Mar 2009

WEATHERGRAM
YOTREPS
Issued 8 MAR 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.

Well I've just finished attending the Auckland Boat Show, so I'll keep
this brief.

LAST WEEK
I can vouch for the intensity of the squash zone over northern NZ that
I mentioned would hit last Wednesday/Thursday when the Chathams High
reached 1030+---winds were strong enough to briefly close one of the
Boat Show's pavilions and to turn off one of the coffee machines for 3
hours. Ouch. We got that front on Saturday too, but it was so weak when
it passed over Auckland it could only be seen by the discerning eye---
it re-intensified over Bay of Plenty on Saturday afternoon with
thunderstorms that took out power in Tauranga when many were watching
rugby.

In passing, I think the southwest change that reached Auckland after
that front is one that provides/announces a reasonable window for
sailing from Northland to Tonga- but it is still really too early to go.

I admit I wasn't expecting that convergence zone/squash zone combo over
the Queensland coast to cough up with a TC until maybe mid March... but
HAMISH has formed and has one of those CAT 5 eyes that can do a lot of
damage. It is moving southeast at present, parallel to the coast.
Hopefully it will maintain this track and stay offshore, and as it
encounters a cooler sea, it'll weaken - this may take til Wednesday.

TROPICS
The South Pacific Convergence Zone SPCZ is active with HAMISH near the
Queensland cost. There's another branch of lesser activity from
Solomons to New Caledonia, and another form Tuvalu to Tokelau, and some
disorganised convergence over French Polynesia. Once HAMISH fades these
zones are likely to amalgamate but the models are not expected any extra
activity this week.


SUBTROPICAL RIDGE
A large HIGH 1024+ is in the Australian Bight, slightly south of the
normal subtropical latitude for March, and that's a sign that this LA
NINA is still influencing our weather. This HIGH's centre is moving
slowly east along 50S - slowly rising to 45S - and should cross the
South Island on Sat 14 March. There will be a squash zone on the
northern side of this HIGH near 25S between it and HAMISH (OR THE
REMAINS OF Hamish). In the process of this slow migration, it is
expected to nose a ridge into the central and northern Tasman Sea on
Monday, but this nose should weaken away on Tuesday as a LOW below
980hPa moves northeast out of the southern ocean to east of Chathams,
deepening to below 960hPa by Saturday.

SO A POLAR BLAST of COLD SOUTH TO SOUTRHWEST WINDS (between HIGH and
Low) should cross the South Island late Tuesday/Wednesday and North
Island on Thursday. It is likely to bring a taste of snow to the
southern mountains, but soils are still so warm that the snow'll melt
away quickly.


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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