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

08 August 2009

BOBGRAM7 issued 9 Aug 2009

Issued 9 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.

During July the warming trend in the Pacific Equatorial Ocean exceeded
the threshold that is sufficient for this to be called the beginning of
a new El Nino episode. Since then this warming trend seems to have
stalled. As far as the weather patterns are concerned (looking
retrospectively) there hasn't been much sign of an El Nino yet. Its
normal for the atmosphere to lag behind the ocean like this. The
seasonal outlook is for some El Nino activity to show itself in the
South West Pacific during the coming spring-- Basically the weather
patterns will likely be drawn closer to the equator, with lighter trade
winds and with the South Pacific Convergence zone shifted northwards and
eastwards. It is still too early to draw much idea of the coming
cyclone season--- The overhead sun doesn't get to 10S until November,
and that's months and months away, and things can change. However,
since anxious cruisers like to worry about these things, if El Nino is
around in November then some tropical cyclones (which seem to like to
form on the SPCZ) may likely form in the Samoa to French Polynesia zone,
so that's a zone worth moving away from beforehand.

There is a burst of westerly/southwesterly winds in the NW Pacific about
the Philippines, and this area will be a possible area of enhanced
convection and breeding area of lows. The ITCZ is active to southeast
of Hawaii, and anyone near there needs to stay tuned to TC FELICIA's
update-however it looks as though it may fade as it approaches Hawaii.

As for the South pacific - well, this week is not showing any El Nino
signs. The South Pacific Convergence Zone SPCZ, is lying from Papua New
Guinea to Northern Vanuatu/Rotuma, with another branch lying from Niue
to south of French Polynesia. The western branch may move south this
week and reach New Caledonia area or between New Caledonia and Fiji by
the end of this week--- helping form a low between Fiji and NZ around
13-14 August.

A big fat High near 1040 hp over Chathams is expected to move slowly
northeast and fade this week -- that will enhance the easterly winds
along 20S from French Polynesia to Tonga.

A weak High is marching steadily along 55S to south of the Australian
Bight and looks as though it will cross the South Island on Wed/Thu
12/13 Aug and then join the BFH. Another weak high is expected to form
over southern QLD on Sat 15 August but then fade. So I hope people have
been enjoying this BFH while it has visited us, for it is unknown when
the next High will get to NZ.

Lows are forming in the Tasman Sea, on the western shoulder of the BFH.
The BFH is such that these lows are being shunted south out of the
Tasman, but there are strong NE to N winds over NZ, between the Tasman
and the BFH.

Around Thursday or Friday the SPCZ may help form a subtropical low to
north of NZ, and by then the BFH may be sufficiently off to the east,
so that this low can run southwards right across the North Island on
Friday Saturday Sunday. Avoid.

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