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

18 July 2009

BOBGRAM7 issued 19 July 2009

Issued 19 July 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.

The South Pacific Convergence Zone is gradually reassembling itself
after a quiet week last week. Convection has been active about
northern Papua New Guinea and over the Solomons... and also in an
unusual band between 2 and 6S from 140 to 160W - this could be extra
convection triggered off by warm seas near the equator. There is
currently an amazing blob of convection near EQ q65 to 170E, with
squally gales and westerly winds on its northern side/easterly winds on
its southern side---a sign of El Nino kicking in - and is more likely to
go north rather than south.

El Nino is pretty much here now as far as the equatorial Pacific ocean
temperatures are concerned, but, so far, just a few signs in the
atmosphere. One of these is a distinct dropping off in wind speed in
the trade winds between 100to 120W fro those sailing from Galapagos to
Marquesas to think about.

This week, the SPCZ is expected to start re-building itself, and extend
from Solomons to Tuvalu and Tokelau maybe to Rotuma and Futuna.

There is a weak trough moving east across Fiji on Monday and Tonga on
Tuesday --- the tropical extension of a front that crossed Northland on
Friday and Gisborne on Saturday. This trough is forecast to develop a
Low near 25S on Tuesday, as it crosses Niue. That Low should be taken by
a jetstream quickly S=southeastwards and may well bomb on Wednesday near
30S 160E as its trough crosses Southern Cooks. Standby for some squalls
from this passing trough.

A subtropical HIGH around 1024 hPa has formed in west Tasman Sea and is
about to go east along to 25 to 30S zone. There will be a bunching of
isobars on its northern side as it travels--- a squash zone ----for
Coral Sea and Vanuatu on Monday and Tuesday, for Fiji from Tuesday to
Thursday, for Samoa from Wednesday to Saturday, and for Southern Coos
from Thursday to Saturday. These are good days for windsurfing, not so
good for fishing.

That High travelling east along 25/30S will bring a touch of spring-like
weather to NZ for the start of this week, but more cold air from the SW
will likely remind us of winter again from mid to late week.

For Monday and Tuesday, west to NW winds - shower sin the west and
milder dryness in the east. Ah, I can see daisies in the lawn at last.

On Wednesday a southerly is forecast to rip across Tasmania and cold air
entering the south Tasman should mould a low. This Low is forecast to
move northeastwards across North Island on Thursday and Friday, and then
(over the weekend as it moves off to east of NZ) it may deepen and
re-curve to the E then ESE as it goes past 180. It is followed by a
cold SE wind change that will linger near Gisborne on Saturday and

The following HIGH is NOT at 25S - it is more likely to be at 45S (so
breaking up the spring-like pattern for a while). It should bring a
period of light winds to Tasmania on Thursday and Friday, to South
Island on Saturday and Sunday, and to North Island on Monday 27th.

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