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

16 August 2008

BOBGRAM7 ISSUED 17 August 2008

Issued 17 August 2008
Bob McDavitt's ideas for South Pacific sailing weather.
(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

South Pacific Convergence Zone SPCZ is going through a quiet time at
present and has broken into a few disconnected branches. One stretches
from Papua New Guinea to Vanuatu and occasional feeds showers over
northern parts of Fiji. Another stretches from between Samoa and
Tokelau to the Northern Cooks and occasionally breeds showers between
Tuvalu and Wallis/Futuna in the west or over Tuamotu group in the east.
This means that those hopping west from French Polynesia should go via
Aitutaki or Niue rather than the Suvarov way.

Easterly winds dominating the whole South West Pacific, both north and
south of the SPCZ. There is likely to be a squash zone of enhanced
trade winds over western half of Coral Sea (and the Great Barrier Reef)
especially on Wednesday and Thursday in response to a HIGH then crossing
the Tasman Sea. Not comfortable.

Some of the SPCZ occasionally connects with the mobile east-ward
travelling mid-latitude troughs. One of these connection-troughs is
likely to visit New Caledonia on Friday and Saturday 22-23 August, and
may affect parts of Fiji/Tonga on Sunday 24 August. These troughs
bright light variable winds and a few tropical squalls. Today's
computer output is picking intense squalls around the NW of New
Caledonia on Friday 22 August but this may change by then.

It is time for another HIGH to makes its way eastwards across the Tasman
Sea - and the next one is forecast to form in the Tasman near 30S on
Tuesday. This HIGH should cross Norfolk Island on WEDNESDAY and
Kermadecs on Friday and be south of French Polynesia on Sunday 14 August
UTC-there will be enhanced trade winds at 20S to north of this High.

The High is expected to be followed by a trough that will cross reach
Sydney on Thursday then cross the Tasman and then NZ on Saturday/Sunday
(yep another wet Saturday). AT this stage the HIGH following this
trough (next week's HIGH) is expected to take the 35SOUTH latitude.

So, there are reasonable weather patterns for crossing the Tasman
either way : next week's HIGH may be a slightly better choice for
sailing westwards to Brisbane, and this week's trough does offer an
opportunity from sailing eastwards across the Tasman.

Heaviest snowfalls in the Arthur's pass and Ruapehu areas of NZ since
the early 90s (and the Pinatubo eruption) - caused by a deep LOW that
stalled over southern NZ taking southern ocean air and swinging it north
into the Tasman Sea then in a westerly flow onto NZ. We meteorologists
call it mmP or modified maritime Polar (kiwi will get the pun about mmp
in an election year). But nope, this winter, in spite of all the wind
rain and cold doesn't get to break any records or hop on any medal
podium - we've had wetter, colder and windier winters in NZ. It's just
the snow that stands out, and that's due to mmp.

A system forming over the North Island today (Sunday) will deepen into a
LOW below 990 east of the North Island on Monday and this system is
forecast to LOOP and deepen further on Tuesday, exposing eastern North
Islanders to a sting of enhanced wet cold southerly winds (avoid).
Thursday is the best day of the week in NZ for light winds and a
reasonable sunny day for golfers.
The next trough is likely to start off on Friday with heavy rain for the
Southern Lakes with its NW flow on Friday, followed by west to SW
showery weather on Saturday and Sunday. Avoid.
Best days to depart/sail from northern NZ for Tonga are Monday/Tuesday.
Best day to depart/sail from Tonga to NZ is Tuesday (for a vessel
capable of up to 6kt).

The terms used here are more fully explained in the METSERVICE Yacht
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