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

13 September 2008

BOBGRAM7 issued Sunday 14 Sep 2008

WEATHERGRAM
YOTREPS
Issued 14 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
place).

TROPICS We are now approaching the equinox -it will be on 23 Sep and
then the days in the southern Hemisphere will be longer than the nights
and soon after that I will start to give out my ideas for the coming
South pacific cyclone season. Things are still in the "non-cyclone"
season mode with trade wind easterlies over the whole area and no sign
yet of any equatorial westerlies.

South Pacific Convergence Zone SPCZ is 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 Niue to Southern Cooks and
southern parts of French Polynesia. Not much change is expected in
these areas during this week.

The main thing to consider, if Island-Hopping this week, is the
subtropical trough currently crossing Fiji. Its rain band should reach
Tonga on Monday UTC and Niue on Tuesday and then fade over Southern
Cooks by Thursday. It goes eastwards even in the trade wind belt north
of 25S by virtue of the westerly winds it has about and above its
clouds. The surface easterly winds turn NE and ease as the trough
approaches , there are some squally tropical showers as the trough
crosses and then the winds fill in again as steady SE winds as the
trough moves off to the east. If you are watching this trough's
footprint by means of Grib winds do NOT be led astray but the light
winds it shows with this trough - The computers cannot resolve the
tropical squalls and each will be able to produce 30 knots in 30 minute
bursts. SO if you are intending to sail across this trough, then go on
squall watch.


SUBTROPICS /TONGA and FIJI
A LOW is developing in this trough near Kermadecs today / Sun 14 Sep /
and should wander off to the south. SW to Southerly winds on the
western side of this LOW are likely to affect Fiji and Tonga until Wed
17 Sep so best to wait for these to swing back to SE winds before
sailing west in this area.


TASMAN/NZ
Spring grass growth should flush in NZ this week.

A trough and front crossing Tasmania today, 14 Sep, should cross South
Tasman Sea on Mon and Tue, proceeded by a NW flow that will be wet for
Southern Alps and dry and warm further east over the South Island. The
front should cross NZ on Wed followed by a SW flow on Thurs and Friday.
Avoid this front.

A HIGH moving east across Australia is expected to follow that front and
cross the Tasman Sea on Wed/Thu /Fri along 35S and the cross central NZ
on Sat Sun 20/21 Sep. This HIGH should be followed by another NW flow
then another front early next week - a typical spring pattern


The terms used 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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