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

29 August 2008

BOBGRAM7 issued 24 Aug 2008

WEATHERGRAM
YOTREPS
Issued 24 August 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
place).

TROPICS
South Pacific Convergence Zone SPCZ had another quiet week and is most
active along 10South - Papua New Guinea to northern Vanuatu and southern
Tuvalu to Tokelau to Northern cooks to northern Tuamotu. This still
means that those hopping west from French Polynesia should go via
Aitutaki or Niue rather than the Suvarov way.
The subtropical ridge, to east of 180, is strongest along 30S, so the
trade winds are enhanced about half-way in-between, along 20S.

Some of the SPCZ occasionally connects with a mobile east-ward
travelling mid-latitude trough. One of these connection-troughs is
crossing New Caledonia today, 24 Aug, and should visit Tonga on
Tuesday/Wednesday, Niue on Thursday and Southern cooks on Friday UTC
this week. These passing troughs are preceded by a period of light
variable mainly NE winds, accompanied by a few tropical squalls, and
followed by a re strengthening of the SE trade winds. There has been a
near weekly rhythm to them recently.

SUBTROPICS
It is time for another HIGH to makes its way eastwards across the Tasman
Sea - That one over eastern Australian coast today (sun 24 Aug) is
expected to weaken away as it moves NE across the Tasman Sea towards
Norfolk Island on Monday to Wednesday - Just not enough oomph. A weak
front is forecast to move east across Tasmania on Tuesday UTC followed
by a HIGH with oomph, that should cross the south Tasman Sea at 45S on
Friday and the South Island on Sat and be east of North Island by Mon 1
Sep.
Early next week there are signs that a low /trough may form in the Fiji
area and wander southwest towards eastern New Caledonia.. Not sure about
this yet, but if it does happen then there will be a squash zone of
enhanced easterlies between this trough and that HIGH , mainly around
30S between Kermadecs and Norfolk Island. Maybe worth avoiding.

NZ/TONGA AREA
It is still winter here in NZ, but the deepest depth of cold was , it
seems, 9-10 August, just after the start of the Olympics if you can
remember back that far. The LOW crossing North Island Monday/Tuesday is
followed by a southerly affecting southern North Island mainly in
Tuesday/Wednesday. The remainder of the week is dominated by the
incoming HIGH.

Nothing much to watch out for, in sailing to/from Northland this week.
Just remember about the possible Kermadecs to Norfolk squash zone that
MIGHT form early Sept.

The terms used here 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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