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

25 July 2009

BOBGRAM7 issued 26 July 2009

Issued 26 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 another quiet week last week. Convection has been active about
northern Papua New Guinea and over the Solomons... and occasional
convection is appearing around Tuvalu and Tokelau, and around Southern
Cooks. Fiji had a dry week last week.

This week, the SPCZ is expected to start re-building itself in the
northern Coral Sea and extend towards New Caledonia /Vanuatu.

Much of the South west Pacific will have fairly steady trade winds this
week, but there will be some variations.

The tropical extension of a mid-latitude trough is affecting Southern
Cooks over next few days (27 to 29 July UTC), and this is expected to
affect southern Island of French Polynesia from 30 July to 1 Aug.

As for those sailing from Galapagos to Marquesas: the next week or two
is looking OK, with east to southeast winds maintained OK as Highs
travels east along 30S from 140W to 100W... These winds may weaken for a
few days around 2 Aug as that trough (between Highs) travels east along

The subtropics east of 180 is currently dominated by a large low that
formed near Kermadecs after last few days. This low is forecast to move
east along 35S sucking away some of the force in the trade winds
further north as it wings along this path - south of Niue on 26-27 Jul,
and south of Cooks on 27-29 July.

Following this Low a new HIGH is forecast to form east of Chathams by 29
July (from the ridge that is moving east across NZ this weekend). This
HIGH should build and travel NE to 30S 140W by 2 Aug... forming a squash
zone of enhanced trade winds over French Polynesia

Trough is crossing the Tasman Sea and is forecast to cross NZ on
Wednesday, followed by a disturbed westerly flow... that will be SW on
Thursday, a front over the South Island on Friday, westerly on Saturday,
and northwesterly by Sunday.

This disturbed westerly flow is expected to bring heavy rain to the
Southern Alps, and dry mild weather to the eastern South Island. A new
subtropical High cell may form between Lord Howe and Norfolk Island on
1-2 August, bringing another settled weekend (like this one has been) to
North Island.

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