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

16 August 2009

BOBGRAM7 issued 16 Aug 2009

Issued 16 August 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.

After a few weeks of atrocious weather, it now seems to be settling down
now around South China and Philippines. In fact the coming week should
be drier than normal there, but TCs are still being produced on the
ITCZ - one near the dateline (TC MAKA) and another SE of Hawaii (TC
GUILLERMO, should go NW and get north of Hawaii) so take care there.

As for the South pacific - well, the main part of the South Pacific
convergence Zone SPCZ seems to have settled to be slightly north of
where it was a few weeks ago, and is now over Solomons to
Fiji/Wallis/Futuna to Tonga area. It isn't expected to travel much from
this placement over the next week or two, and that means some parts of
this zone will be getting real soggy. Vey likely an intensification of
activity may pulse along the SPCZ late this week, over Solomons on
Friday and reaching Tonga/Niue on Saturday /Sunday 22/23 Aug. Avoid.

There seems to be an increase in convection in the zone along 5S to 10S
from 180 to 140W. Over the next month or so the overhead sun will be
heading for the equator, and this typically causes a twinning of the
ITCZ with a mirror zone between 5 and 10S--- so maybe this mirror zone
is starting to form. I'll keep an eye on this.

There has been some blocking but its eased now, so we are in for a
change in weather pattern.

The remains of last week's big fat high BFH are today around 1032 near
35S 160W, bringing enhanced trade winds on its northern since to between
southern French Polynesia and southern Cooks - all fading away by end of
Tues 18 Aug GMT as that high continues on its easterly migration.

Two more highs will enter our arena this week, but not as big as last

The first is already entering the North Tasman Sea and should feed a
squash zone in the northern Coral Sea until Tuesday that may briefly
stretch east to Rotuma.

The second should be larger than the first and bud off Australia and
expand across the central Tasman Sea on Wednesday, with a strong SSE
squash zone over New Caledonia and the full Coral Sea. This high is
likely then to contract northwards and become a slow-moving high that
will hug 30S and not reach 180 until end of next week /29 Aug. It
brings some reliability to the weather I suppose-and this weather
pattern is typical of El Nino.

Between these migratory highs are lows and troughs... one is bringing a
southerly and welcome rain to eastern North Island tonight.

Next front is expected to fracture as it moves from Tasman Sea onto NZ
on Tuesday. There will be some wicked southerly winds following it, may
bring more welcome rain to eastern NZ (and snow to the mountains), and a
sling shot to anyone wanting to sail northwards.

This should be followed over NZ by a one-day-ridge on Thursday 20 and
then a disturbed westerly flow from Friday 21 to Wednesday 26 August
(avoid sailing with these), with an outlook of another one-day-ridge on
Thursday 27 Aug and then very strong NW winds at the end of next week,
bringing a warm spell that will end winter.

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