BobBlog

WEATHERGRAM
YOTREPS
Issued 25 May 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 of weather maps, so please fine-tune to your place. Dates
are in UTC unless otherwise stated.

Scott Donaldson has had made good progress in the past week kayaking across
the Tasman Sea. Tonight he is in 4 to 5 metres swells and 20 knot winds from
the SW, and managing to make way to the southeast.

The Ocean: The warmer the sea the quicker it evaporates, tossing water
vapour into the air, where is rises and cools into cloud. The equatorial
Pacific region hosts the warmest sea on the planet. Thus its sea surface
temperatures SST is a factor in the running of planetary weather engine.
An index for this is NINO3.4 and its abnormalities tend to influence changes
in clouds along the equator and thus tweak the latitude zones of weather
around the planet. Recently a lot of extra heat has been stored in the upper
depths of the equatorial Pacific Ocean and some of this is now reaching the
surface near the Galapagos.

TROPICAL TOPICS
The new hurricane season in northern hemisphere is meant to start at the end
of this month and already HURRICANE AMANDA has started off the west coast of
Mexico:

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
South end of SPCZ is expected to visit Fiji on Monday 26 May UTC, Tonga on
Monday/Tuesday, Niue on Wednesday and Southern Cooks on Thursday/Friday UTC.
Another part of the SPCZ is likely to spread south onto Tonga again around
Sat 31 May UTC.

STR= Sub-tropical Ridge
The STR is north of its normal position for this time of the year in
Australia, and mainly at its normal position between 30 and 35S across the
Pacific.
Tonight a high has budded off from the Antarctic ice shelf and travelled NE
into the South Tasman Sea/, shovelling ice-chilled SSW wind flow onto
Southern NZ. This cold high is expected to travel NE cross the Tasman Sea on
Monday and northern NZ on Tuesday and then travel east along 30/35S into the
Pacific.
The next HIGH is expected to move off Australian coast into central Tasman
on weekend of 31 May/1 June

Departing from NZ to the tropics
A cold southerly/SW flow over northern NZ on Monday is good for going north,
Light winds over northern NZ on Tuesday with passing HIGH, not so good for
sailing.
Then a large and intense trough is expected to approach North Island on
Wednesday, with increasing NW winds, and cross the Island on Thursday with a
period of squally showers. Not good for departure.
The decreasing SW flow on Friday may offer a good weather pattern for
departure  but such a departure might encounter a new trough over the
Tongan area the following week, too far away to tell at this stage. A Friday
departure might work ok.

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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