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

26 April 2009

BOBGRAM7 issued 26 April 2009

Issued 26 APR 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.

South Pacific Convergence Zone SPCZ has been weak in the past week,
strongest in central Coral Sea (320 mm/week) and between New Caledonia
and Fiji (250mm/week).
This branch of the SPCZ should be slow-moving this week. It may become a
bit more active than last week but the cyclone season seems to have
wound down now.

There is another branch of the SPCZ near Niue this weekend and this is
expected to move east across Southern Cooks this week.

That zone of convection mentioned last week mainly from 5 and 8S between
Marquesas and Galapagos is still there, but is weakening.

The trade winds easterlies are robust between New Caledonia and
Queensland this week, (they were weak there last week).

The Big Fat high BFH that spent this weekend over Chatham Islands is now
moving slowly east along 40S and there is a squash zone between it and a
trough from Kermadecs and Niue, mainly along 30S. By the end of this
weak the BFH is likely to be east of 120W, and that trough is likely to
have grown to a large LOW and travelled south to 40S along 160W. This
may become useful for sailing from NZ to Tahiti, but only if you wait
for the current NE flow over northern NZ to turn northerly (that should
happen on Tuesday).

It was a good-old southern-ocean southerly that brought rain to Adelaide
for ANZAC day, and the associated trough/low is expected to cross NZ on
Wednesday. This will be preceded by several fronts and a NW flow,
possibly dumping 400 to 500 mm of rain over the Southern Alps in 3 days,
with relatively warm days in eastern areas.

On Thursday, what follows the trough/low is a cold southerly over NZ,
but this may not bring much rain to Nelson/ Hawke's Bay Gisborne, our
driest areas.

On Friday the next HIGH is expected to cross Campbell Island, allowing
a southeast change to bring some wind and rain to eastern North Island
on the weekend of 2/3 May - double check this nearer the time as it may
delay that "perfect departure from Northland to the tropics".

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