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

26 March 2011

BOBGRAM7 issued 27 March 2011

WEATHERGRAM
YOTREPS
Issued 27 March 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.

TROPICS
La NINA is weakening. The Southern Oscillation Index 30day running mean
moved from 1.95 on 20 March to 1.85 on 25 March.

Hmmmm, developments over the past week in Southwest Pacific came from
the east rather than the west (which was where I was looking). A
rejuvenation of the South Pacific Convergence Zone SPCZ spread westwards
along 15/20S from Tahiti to Fiji, and there it stalled and ganged
together on Thursday to form TC BUNE (in Fijian this is pronounced
MBU-NAY).

BUNE has since then been creeping southwards and feeding well on
tropically warm seas, ending slightly west of 180 (the anti-meridian).

This week the main SPCZ is likely to reform from Solomons to Tuvalu to
Tokelau to Northern Cooks, and it might move slowly south.

There is a lot of convection over northern Australia, and strengthening
trade winds over Queensland... There may be the development of a
tropical depression near NW Australia.

SUBTROPICAL RIDGE:
HIGH 1 is a typical La Nina high - wondering along 43S - on Sunday 27
March it is at 140W and moving off to the east.

HIGH 2 is expected to taking a middle route - crossing the Tasman Sea at
40S on Monday 28 March and then being diverted across South island and
along 45S as it works itself east around BUNE on Tuesday 29 March. An
interesting dance.

HIGH 3 is expected to be slightly further north, crossing Australian
Bight and peaking at 1030 on Wed/Thu 30/31 March, then New South Wales,
northern Tasman Sea/northern North Island on Friday/Sat 1/2 March at
1025 or less.

NZ AREA

A trough crossed NZ over the weekend a, leading in a SW flow fresh from
the southern ocean, along with some heavy swell, easing on Monday as
HIGH 2 approaches.

BUNE is now moving out of the tropics into cooler seas so can not
produce high enough clouds to keep its central ring going, but will take
a few days to unravel. That SW flow is expected to reach BUNE on
Tuesday and this may help expand its area of gales and rain. On Mon and
Tue 28/29 March it will dance with a passing anticyclone-they may waltz
or they may tango, we will not really know until it happens. One
scenario is for this to be a tango, moving the wind and rain close to
eastern North Island on Wed/Thu 30/31 March. There are many other
possible outcomes that keep the wind and rain offshore the mainland, so
if this affects you then get updates.

Easterly Swell from BUNE is likely to start reaching North Island
eastern coasts from Tuesday and peak on Wednesday.

Cold front is expected to reach South Island on Thu 31 March and North
Island on Friday 1 April; the NW flow ahead of this system should kick
remnants of BUNE away. The westerlies of the southern ocean are now
creeping steadily north.

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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