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

27 February 2010

BOBGRAM7 issued 28 Feb 2010

WEATHERGRAM
YOTREPS
Issued 28 Feb 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TSUNAMI
The Tsunami ripples from that 8.8 Chilean quake seem to have mostly done
their dash now. If you are on Internet and are quick enough you can see
them at http://bit.ly/nzwaves . My condolences to anyone who suffered
from the quake and its waves, this planet can indeed be a rough place to
live at times.

TROPICS
SARAH started as a tropical depression with enough squally gales to
damage Penryhn Island in Northern Cooks early last week and has been
moving slowly south for much of last week until finally earning its name
a few days a go. It has now lost its top clouds and visible imagery
show a well-wound up compact spiral of cloud, slowly and erratically
looping. If it comes much further south it will likely get ripped apart
in an unfavourable environment. It still has gales and squalls but
these too should fade over Southern Cooks over next few days.

Computer models are picking another tropical low (or two) likely to form
near the south end of the main Islands of French Polynesia PF around 3
or 4 March UTC. This system should deepen as it moves south, so that
winds over PF are likely to be from the northwest for much of this week-
and squally.

A new pulse of extra tropical convection visited Northern Australia last
week and has culminated is a deep low over the mainland of Australia.
This system has too much friction and not enough access to sea-warmth so
is not expected to become a tropical cyclone, but is windy and wet
none-the-less and should spend this week heading south across central
Australia merging on the south-side over Melbourne on Thu 4 March with a
trough crossing the Australian Bight.

The South pacific Convergence zone has been concentrated near Northern
cooks for past week or sop, and scattered and disorganised elsewhere.
Well, this week it is likely to reform across the northern Coral Sea/
Solomons/Tuvalu/Samoa. In fact a tropical Low is expected to form on
the SPCZ and between Vanuatu and Fiji but Tue 2 March and then cross
Fiji on Wed 3 March and then drift south past Raoul Island on Fri 5
March, possibly getting close to northern NZ over the weekend of 6/7
March or early next week. This system isn't expected to become a
full-on cyclone but does deserve respect.

There is a good risk that another low may form near Vanuatu next week ,
8-12 March and that one may become a tropical cyclone, more about that
in my next weathergram.

SUBTROPICS

The subtropical ridge is strong and hugging 40S to 45S in the South
Pacific.

The High centre east of the North Island today, sun 28 Feb, should
steadily wander east this week along 40-45S reaching 120w by about sat
6 March, sort of a repeat of last week. AVOID the squash zone between
this High and that low over southern PF

The next HIGH should enter the central Tasman Sea on Wed 3 March and get
defected south across the South Island on Fri 5 March. AVOID the squash
zone between it and Low near Raoul Island or northern NZ on Sat 6 March.


NEW ZEALAND

Between the two Highs is a transitional trough. This one seems to have
missed (just/today) the opportunity to get an injection of energy from
the heat trough/monsoonal low over central Australia, so should cross NZ
on Tuesday 2 March, containing two fronts, first is preceded by NW winds
and second is followed by SW winds. There may be some heavy rain in the
west with the fronts. Winds are likely to turn S over the North Island
on Wed 3 March and SE/E for rest of week - with HIGH to south and Low to
north, a recipe for strong winds.


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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