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

06 September 2008

BOBGRAM7 issued 7 Sep 2008

Issued 7 Sep 2008 NZST
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 steady in strength and patchy in
coverage... It is strongest about Papua New Guinea and Solomons...
Another burst of activity at times between Tokelau and Samoa, and
occasionally over north Tonga, then it sort of stretches from about
Suvarov to midway between Southern Cooks and French Polynesia. There
has been a squash zone between the SPCZ and a Big fat high recently-this
squash zone still affects Southern Cooks to Niue with strong trade winds
and rough seas.
Highlight of the coming week to look for is for a build up in activity
near Suvarov on wed 10 Sep UTC moving South onto Southern Cooks by sat
13 UTC, There will enhance that squash zone even further, with tropical
squalls on its north side and steep big swells on its south side, so I'd
say it IS NOT the week to sail from French Polynesia to Tonga, unless
you like riding a bucking bull.

When this system moves off to the south early next week, it may pave the
way for a Low to possibly form about or south of Niue then SW towards
Niue early next week. After that we may have a good weather for sailing
westward ho!

Rest of the South Pacific between Tonga and Australia is looking OK this
week-a gentle subtropical ridge along 30S and average trade winds mainly
along 20S. Computers are picking some kind a drawn out surface trough to
form south of New Caledonia and extend towards Kermadecs by Friday---
probably caused by an upper Jet Stream and - this trough is forecast to
cross Fiji and Tonga on 14 and 15 Sep utc, but not much in it until it
possibly forms that Low south of Niue early next week.

In a reversal of pattern back to winter NZ had a ridge over the weekend
(frosty in places) and is following up with a LOW from the Tasman Sea
this week. The frontal zone is likely to cross the North Island on
Monday and may linger across the south end until Thursday and the Low
itself slowly works its way in pieces across central NZ. On the north
side of this LOW, over the North Island, will likely be squally
westerlies from Tuesday til Thursday. A Southwest flow should clear the
weather over NZ on Friday and then the outlook is for another ridge of
light winds for next weekend.

Conditions should be OK for sailing from NZ to Fiji/Tonga after the
Monday front, but wait til Friday if sailing NZ/New Caledonia.
Best day this week to sail Tonga to NZ would be, depending on your
cruising speed, around Mon/tue utc -so that you encounter that trough at
around 30S on Fri 12th, and time you arrival in NZ with a SE flow
maintained by that weekend ridge.

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