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

03 May 2009

BOBGRAM7 issued 3 May 2009

WEATHERGRAM
YOTREPS
Issued 3 MAY 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.

TROPICS
South Pacific Convergence Zone SPCZ is in the zone from Tokelau
southeastwards to in-between Northern and Southern Cooks and French
Polynesia. Trade winds are weak east of the date line, with a
subtropical ridge near 15S (wow, that's way north), and huge LOWS
dominating between 30 and 40 S to east of NZ. So in this area the SPCZ
is behaving like the tropical end of the fronts attached to those lows.
That low I mentioned last week to be lurking to SE of NIUE has had some
fronts and gales around it is finally moving off, but watch out, it
looks as tho' another may behave much the same Thu 7 to Sat 9 May UTC.

West of the dateline, things are closer to the norm, with SPCZ from
Solomons to northern Vanuatu, and fresh SE trade wind sin the mid Coral
Sea between the SPCZ and higher pressures off Southeast Australia.
Conditions in this area are looking steady for good sailing.

That zone of convection mentioned last week mainly from 5 and 8S between
Marquesas and Galapagos is now fading away.

SUBTROPICAL RIDGE STR
A fortnight ago we had a big fat high in the STR. Now the STR is going
through a very weak week. There are highs moving across the Aussie
bight, but they are all weakening in the Tasman Sea - it may be a
fortnight (mid May) before we see the next high reach NZ.

NZ AREA
The first cold southerly in May is usually enough to shiver the timbers
of cruising yachts in Northland so they all want to leave for the
tropics. A similar autumn occurrence in the US is called the
Californian Flush, so it isn't a great surprise that our "OPUA FLUSH"
has begun.

Since the SPCZ is behaving itself and nothing much is happening in the
tropics (apart from those lows near Niue), the warmth beckons: it does
look as tho the cyclone season had faded fully, fingers crossed.

Those departing today on Monday should have a good voyage north. Others
should try and get away before noon Tuesday if they wish to get north
before some incoming heavier swells.

Those waiting til later may have problems--- between the weak STR and
lower pressures to the south the winds are dependable enough: west to
southwest, so no great problems there. The problems are to do with
some LOWS INTENSIFYING over NZ and bringing STRONG/GALE winds and bursts
of HEAVY SWELL. Those swells wander far away from their generating
winds and can be uncomfortable: they will, however, have long periods
once they get north of 35S.

This week there are two LOWS to avoid: The first brings wind and swell
to Northland on Wednesday as it crosses central NZ, then there's a brief
easing on Thursday, then the next brings wind and swell to Northland on
Friday and Saturday. At this stage it is likely to be followed by a
significantly cold outbreak over NZ on Sunday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

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