Bob Blog

WEATHERGRAM
YOTREPS

Issued 09 November 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 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 dived below -10 (Australian units) for
much of September, slightly relaxed for a whole in October, and is now
diving more negative again.

The Ocean
The amount of heat that is being stored in the sea in the Eastern Equatorial
pacific has also increased, as measured by the NINO3.4index.

The chances of a full blown El Nino episode over the next few months are now
considered to be no more than 58% (less than this time last month).

TROPICAL TOPICS
Tropical cyclone activity has now reduced to a few possible potential areas.

Weekly rain maps over the past fortnight show some local regions of intense
rain due to a few tropical cyclones. There also has been a notable build-up
of convection in the past week between India and Indonesia. Not much change
in South Pacific.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is steady in position and fluctuating in intensity. Mainly over the sea
between Solomons and Wallis /Futuna then along 15S.
The Low that has formed between Fiji and New Zealand near 25/30S 180 is
expected to travel SE and fade-away by Wednesday.
A Low is expected to form near 30S 140W by Tuesday and then travel to east
then south east.

STR= Sub-tropical Ridge
High is expected to cross Tasmania on Tuesday and then travel NE towards 20S
between New Caledonia and Kermadecs by the end of the week, bringing a zone
of light winds.

Between the tropics and NZ
At north Minerva a front visited on Saturday accompanied by squally showers
and strong E/NE winds. As the Low in the region travels east/southeast over
the next few days, expect strong WNW winds there from Monday morning to
Tuesday morning, peaking pre-dawn on Tuesday. Then expect moderate SW winds
there on Tuesday and Wednesday. After that the STR is expected to get north
of Minerva for a few days so that it has W/SW/S winds on Thursday and
Friday, finally reverting to SE this weekend.

An intensifying trough is expected to cross NZ on Monday and Tuesday,
followed by an outbreak of strong to gale SW winds in the Tasman Sea on
Wednesday and Thursday. These winds are expected to help propagate an area
of big SW swells (from the Southern Ocean) that spread NE into the region
between NZ and Fijias far north as 25S on Thursday and 23S on Friday.

Voyages from New Caledonia /Fiji/Tonga to New Zealand should wait for the
Low to go away by late Tuesday, and then try and avoid the big swells on
Thursday /Friday. This can be done with a Friday departure and a few
waypoints.

AT this stage, the outlook next week over NZ looks reasonable for voyages
aiming to arrive there between Tue 18 and Friday 21st ( but this may
change).

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
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