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

19 December 2009

BOBGRAM7 issued 20 Dec 2009

Issued 20 December 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.

Cyclone MICK took with it a lot of the convective energy that had been
building up over recent weeks, and has left behind a very quiet South
pacific convergence zone SPCZ. This zone is now rebuilding along 10S
between Tokelau and Northern Cooks, and is expected this week to shift
more to 15-20S between Samoa and French Polynesia. Computer output
suggests a LOW forming on the SPCZ around French Polynesia on Tuesday 22
Dec UTC and then moving to the south of the group on Christmas Day.

There is still some of the old SPCZ convection around Vanuatu , and this
is expected to wander around the region all week in a disorganised

MICK dived into the subtropics last week and has "stolen" much of the
trade winds and disrupted the position of the subtropical ridge. The
next high roiling in from the west is over the Tasmanian area today and
is likely to take a track more common for highs at this time of the year
- we have the summer solstice on Tuesday 22 Dec= the longest day, and
meant to be the start of the southern most tracks for subtropical ridge.
This High is expected to cross the North island / 40S on Tuesday 22 Dec
and then nose into the South Pacific along 30 to 40S steadily holing
itself together as a single entity until 30 Dec. Reliable and

As this High slides east it will bring the trade winds back from
southern French Polynesia all the way to the Coral Sea. There may even
be a small squash zone on the northern side of this high, along 25 to
30S between 160W and 180 from 23 to 28 Dec.

During a lead up to Christmas over NZ there is a dying southerly flow on
Monday 21 Dec, and then the passage of that High with light winds and
generally settled weather. On Wed 23 Dec, as the High is crossing the
North Island, some converging sea breezes may combine with cold air
aloft to make afternoon heat showers/intense downpours around Bay of

If people here can still remember the weather they had last Fri, 18 Dec,
then it looks like something similar will be happening to then Fri 25
Dec, for that's when the next front, in cahoots with the central
Australian heat trough, will be moving from Tasman Sea onto southern NZ,
preceded by a NW flow, kicking away the High further north. Some
differences also: the NW wind may not be as strong, and in central
Australia by then will be the remains of Cyclone LAURENCE.

Christmas reminds us of the miracle of new creation and the purpose of
living life to it fullest. Festive cheer is part of this process, so
feast cheerfully folks.

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