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

25 October 2009

BOBGRAM7 issued 25 Oct 2009

WEATHERGRAM
YOTREPS
Issued 25 October 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.

NIWA, Fiji Met Service and BoM have all produced much the same outlook
for the coming cyclone season. The El Nino observed in the Ocean was
not having much impact on weather patterns in the atmosphere as measured
by the SOI (until the last week or so). Computers are expecting the
main coupling between ocean and atmosphere to occur around December and
January. Indications are for around 8 cyclones in the South West
Pacific this season (the normal is 9). Countries east of 180 are at a
higher risk than normal. 2 or 3 cyclones may reach at least Category 3
and one may reach at least category 4. The first storm is likely to
develop before the end of December.

There are still cyclones in the Northern Hemisphere-LUPIT near eastern
Japan and NEKI over western islands of Hawaii. Last weeks burst of
equatorial westerlies last extended eastwards to beyond 170E and is
likely to affect Kiribati and Tuvalu this week, affecting west-facing
harbours.

South pacific convergence zone, hugging 10S between Solomons and
Tokelau, has west to northwest winds on its northern side and a squash
zone of trade winds on its southern side along 15S. The SPCZ is showing
signs of moving south and may extend as far south as Fiji by Wednesday
28 Oct, perhaps developing a low between Samoa and northern Tonga that
will extend southeast wards across southern Cooks by 30 Oct UTC... Also
SPCZ may develop a low in the Coral Sea, south of Solomons on 27 Oct
that may stall and then shift west-wards and fade away around 31 Oct
UTC. In any event, the strong SE winds in the central Coral Sea and
expected to last all week.

SO the SPCZ is worth avoiding this week.

CROSSING THE SUBTROPICS and HEADING FOR NZ ... Maybe not this week...
High pressures in the Tasman Sea this week and low pressures to east of
NZ team together so that we have south and southwest winds between NZ
and Tonga over next few days and so no offering of a good sail. This
southwesterly is expected to reach Minerva around Tuesday 27 Oct and
Nukualofa around Wednesday 28 Oct and last around 2 days so that the
next "weather window" for departing from Tonga NZ may open around Friday
30 Oct, perhaps a little later. .

Approaching NZ from New Caledonia or from Australia may be OK this week,
but avoid the SW flow near the North Island on Tuesday and Thursday -
passing fronts may have gale winds and high seas.

In detail: A LOW is forecast to deepen as it crosses central NZ on
Monday and as a HIGH forms in the South Tasman Sea - so that a SW gale
in-between these systems focuses in the area west of the North Island
and reaches a peak Tuesday UTC. The High then fades and stalls on
Wednesday as the Low moves off the east and weakens. But by late
Wednesday and during Thursday a trough deepens east of and over NZ as a
new High builds in the Tasman Sea - in-between will be a vigorous cold
polar outbreak of southerly winds.

That new High is forecast to cross NZ on Sunday and Monday bringing NZ a
break in the SW weather.

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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