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

13 April 2014

Bob's Blog 13 April

WEATHERGRAM
YOTREPS
Issued 13 April 2014
Bob McDavitts 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.

SOI. The Southern Oscillation Index SOI sums up the weather pattern over the
South Pacific as one number. It is based on the standardized difference in
the barometer readings between Tahiti and Darwin.
SOI (30 day running mean) has been in the pink (below minus 10 in the
farmonlineweather.com graph for three weeks and relaxed a little in the past
week.

TROPICAL TOPICS
Tropical Cyclone ITA is visiting the Queensland coast at present and is
expected to move SE towards the North Island by Wednesday and to then travel
south and merge with another low on Thursday/Friday and cross the South
Island on Easter Saturday/Sunday.
In the NW Pacific, ex Tropical Cyclone PEIPAH (DOMENG) has been approaching
central east Philippines over the past few days, but this system is
weakening.

WEATHER ZONES
Panama to Galapagos: There is a NE flow over Las Perlas at present but a
departure now is likely to run into light variable winds in a day or so.
Light and variable winds are expected to dominate proceedings between Panama
and 4N from local Monday until the end of this week.

SPCZ South Pacific Convergence Zone
This is rather disjointed this week and appearing as two distinct zones,
with one around the Solomons and another roughly from Niue to French
Polynesia.
There is still a weak convergence zone along around 5S from around 100 to
130W.

STR Sub-tropical Ridge
The STR is around 40S, its normal location at this time of the year. It has
been knocked out of the Tasman Sea for the first time in around eight weeks.
This should finally allow rain to reach the drier parts of NZ this week.

New Zealand area
There is a Low moving slowly south in the Tasman Sea and its warm front is
expected to bring some rain to New Zealand on Monday. By Wednesday ITA
should have left the tropics and moved SE to be close to the west of the
North Island. During Thursday and Friday this system might re- intensify ;
its central pressure might drop from around 1000 to around 980 hPa, due, I
think, to the density difference between the air it is bringing from
Queensland and the cold air being directed northwards by that other low in
the South Tasman Sea.
This means that a front with gale NE to weaker northerly winds is likely for
the Auckland to Tauranga race this year.
This system is expected to cross the South island during Easter Saturday and
Sunday.
This means that the likely weather pattern for the start of the Solo
Trans-Tasman Race on Easter Sunday is a left-over trough (or two) and then
light winds in a new STR

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