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

02 April 2011

BOBGRAM7 issued 3 April 2011

WEATHERGRAM
YOTREPS
Issued 3 April 2011
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.

We live in interesting times with the weather patterns in transition. NZ
switch from Daylight (summer) time to Standard time today, and the weeks
after the March equinox seem to mark the beginning of a new
meteorological year to go along with the new financial year.

TROPICS
La NINA is making a rebound as isobars lower over North Australia. The
Southern Oscillation Index 30day running mean moved from 1.95 on 20
March to 1.85 on 25 March and back to 2.05 on 3 April.

The eyewall of TC Bune brought torrential rain and gale winds to Raoul
Island, see http://blog.metservice.com/2011/03/the-eye-of-the-storm/.
Then the system unwound and expanded as it rolled away to the southeast
over open sea.

The Intertropical convergence zone ITCZ is showing signs of doing an
equinoctial twining, due to the overhead sun--- one line along 4 to 5N
as normal and another line along 4 to 10S (not normal) all the way from
dateline to Galapagos. Anyone contemplating "puddle jumping" should
wait until at least May for this pattern to fade.

A Madden-Julian-Oscillation MJO has been activating convection over
northern Australia in the past week and is expected to wander into the
Coral Sea this week. This MJO has triggered a tropical depression about
the coast of NW Australia... and this system is expected to be able to
get back to sea next few days and feed off the warmth to possibly grow
into a Tropical cyclone that may make landfall west of Port Hedland on
Thu/Fri 7-8 April. Avoid.

South Pacific Convergence Zone SPCZ stretches from northern Australia
across Coral Sea, New Caledonia, and then to south of Fiji. A jetstream
extends high cloud to south of SPCZ as far as 25 to 30S. SPCZ
(north-edge) is expected to become activated by this MJO during the
coming week, so watch for tropical depressions to develop in Coral Sea
or about New Caledonia. Avoid the Coral Sea this week.

SUBTROPICAL RIDGE:
Two typical autumnal anticyclones to talk about:
HIGH 1 is 1030 tonight near 48S 170W and should wander east along this
latitude to 155W then be forced to take a more southern track by troughs
near 40S.

HIGH 2 is expected to cross Tasmania as 1030 on Tue 5 April then move
very slowly along 40S across the Tasman Sea, expanding to encompass
central NZ from Sun 10 April to mid-next week.

NZ AREA
Between the highs are troughs and lows. A double-barreled trough is
crossing NZ tonight/ Mon 4 April followed by a low deepening off eastern
North Island on Tue 5 April-this should produce southerlies over NZ that
may be cold and wet enough to bring a dusting of snow to Southern Alps.
The disturbed SW flow that follows all this should last until
Friday/Saturday as HIGH 2 approaches.

So we have a week with both a tropical cyclone and the word snow
mentioned - such is autumn.

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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