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

14 February 2009

BOBGRAM7 issued 15 Feb 2009

Issued 15 FEB 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.

Over the past week activity in the South Pacific Convergence zone has
generally declined, but over the weekend a tropical low and associated
wind and rain has formed just east of southern Vanuatu near 19S 171E.
It is moving west and is expected to weaken once it gets wets and
Aneityium and crosses the Loyalties on Monday and New Caledonia on
Tuesday. Avoid.

EC takes this low further south as a separate entity, crossing Norfolk
on 18th and central NZ on Fri 20 Feb, but GFS and NOGAPS models merge it
into a Tasman wide trough during the week. I think the merger idea is
the more realistic.

The low that was mentioned last week to form off Brisbane has indeed
done so, bringing Queensland more wind and rain, but it hasn't evolved
as fast as initially expected. The SPCZ has been strongly active in a
band across northern Australia coast and central Queensland (typical on
a La Nina). The computer models are all coming up with a forecast
that picks that the first LOW near Brisbane will fade. But, offshore, a
large trough with several new centres will form along with an active
rain band, and these will reach New Zealand on Fri 20 Feb preceded by
strong northerly flow and followed by west to SW winds on Sat and
Sunday. Avoid.

There is another weak branch of the SPCZ from Samoa to the southeast---
sometimes over Niue and sometimes over Southern Cooks. It isn't doing

The STR is about as far south as it gets, indicating this current La
Nina at work. We start the weak with a HIGH in the STR about 1030 and
south of Tasmania. This HIGH should move northeast, peeling around
southern NZ on wed 18 Feb. On Thursday there should be a squash zone
between the departing HIGH east of NZ and the incoming trough then in
the central Tasman Sea. Avoid.

After the passage of the trough on Fri20th and the following west to
southwest winds on Sat and Sunday, an new HIGH should reach Tasmania on
Sat 21 and cross the Tasman Sea on Sun 22 and NZ on Mon 23/Tue 24 Feb
with settled weather.

So, at this stage, the forecast for the Patea Fishing competition off
south Taranaki next weekend is for strong West to SW wind, easing away
on the Monday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
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