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

12 October 2014

BOB Blog issued 12 Oct 2014

WEATHERGRAM
YOTREPS
Issued 12 October 2014
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.

The latest NIWA monthly update for a seasonal outlook for the South Pacific
is going for a continuation of drier than normal conditions over most of the
South Pacific area during the next three months.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean)
sums up the weather pattern over the South Pacific as one number. It is
based on the standardised difference in the barometer readings between
Tahiti and Darwin.
It has been negative since July and was near to -10 (Australian units)
during September but is now less extreme indicating that the recent trend
towards an El Nino is now relaxing.

TROPICAL TOPICS
Tropical cyclone activity at present includes Very Severe Cyclone HUDHUD
which has just made landfall over eastern India, VONGFONG which is visiting
Japan, and FAY, a storm in the North Atlantic.
The weekly rain maps show that the heaviest rain is associated with the
tropical cyclones. There has also been some intense rain in the eastern
Coral Sea for the past two weeks.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to weaken this week and be loosely lying from south of
Solomons Islands to between Samoa and Fiji. A few showers associated with a
fading trough are likely over Vanuatu until Monday.

STR= Sub-tropical Ridge
High over northern NZ has managed to arrange just light winds above it and
so is a slow-moving feature and should fade just NE of NZ on Wednesday.
Another HIGH is expected to form over southern NZ on Tuesday and then to
move NE towards 35S 160W, to east of NZ, by end of the week. There is
expected to be a zone of enhanced easterly winds in the tropics and on the
north side of this HIGH-a squash zone.

Departing westwards from Tahiti:
There may be a branch of the SPCZ to avoid over the area especially after
Wednesday.
The squash zone is likely to be mainly south of 25S so should not be too
much of a bother.

Between the tropics and NZ
The vessels associated in the All Points Rally will now be involve in
preparations for their voyage, be it from Tonga, Fiji, or Vanuatu , to
OPUA. The Rally is free of charge (thanks to the sponsors) and helps
participants with planning, weather info, clearance, and seminars on how to
enjoy NZ. See more at www.islandcruising.co.nz/?page_id=1687
and register at www.islandcruising.co.nz/?page_id=1268.
I shall be commenting on windows of weather to get to NZ for these people
here for the next few weeks.
There is a good window for getting to NZ from New Caledonia/Vila/NZ, until
Tuesday anyway. However there is a Low lingering between Tonga and NZ on
Monday/Tuesday so not comfortable to get to NZ from Tonga. As the High that
is forecast to be over NZ this week starts moving off to the east there
should be a northerly flow between it and the next Low that should then be
approaching from the Tasman Sea. This northerly flow can be useful, but the
low itself is no good at all for your voyage. At
present the low or trough is expected to reach NZ on Sun 19/Mon 20 Oct
followed by a brief period of SW winds, then NE winds ahead of a new low.
You can maybe weave between these winds with good timing if you are lucky,
or wait for a better looking pattern.
My choice of weather model for planning purposes is tinyurl.com/ecaus

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
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