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

05 June 2011

BOBGRAM7 issued 5 June 2011

WEATHERGRAM
YOTREPS
Issued 5 June 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.

TROPICS
SOI is in neutral territory and continues to hover just above zero. It
dropped to 0.3 on 22 may and has since continued falling, was 0.18 on 5
June.

No cyclones around at present.

Galapagos to Marquesas: More of the same. Avoid the Equatorial current.
Dive south to around 5S 100W and then head almost due west to 7S 133W
and then head for landfall. No organised tropical showers around.

South Pacific Convergence Zone SPCZ has weakened into clumps --- main
clump is around Tonga and Samoa (as a trough). This branch is likely to
stretch eastwards this week (the reason for this lies with the upper
winds). There is another weak zone in the North Coral Sea. This zone
should grow more extensive and spread southwards this week. And a
minor clump around Tuvalu to Tokelau. A zone of showers over French
Polynesia links with a mid-latitude trough.

SUBTROPICAL RIDGE
HIGH well above 1030 at 37S and south of Southern Cooks tonight has a
spread out squash zone of near gale easterly winds on its northern side.
This High has reached its peak and so has the squash zone. The high
should wander off to the east next few days, so that the fading squash
zone may visit the Australs on Tue to Thu 7 to 9 June.

Weak ridge starts to grow over NZ on Wed 8 June and this should expand
into a new High moving east along 40S to east of NZ over the rest of the
week.

SO, between Northland and Fiji - for the Auckland to Fiji race fleet -
there is a slack subtropical ridge over the next few days, and this
should firm into useful trade winds once this new high grows east of NZ.


NZ/TASMAN SEA
Weak trough crossing NZ on Tuesday followed by that growing high on
Wednesday (mentioned above).

The main feature in our region this week seems to start off as a Polar
outbreak affecting Tasmanian on Tue 7 June. This is expected to deepen
into an intense low off the New South Wales Coast on Wed 8 June and then
broaden across the Tasman on Thursday and finally cross central NZ when
it is decaying on Sat/Sun 11/12 June. If you have full Internet access,
then check this out at http://bit.ly/7daywx .

Australians need to be aware that 5 metre swells may form on western
side of this low on Tue/wed 7/8 June.

WHEN TO DEPART NZ?
With the predominantly northerly flow east of NZ over next few days, it
is as OK as it gets for departing east to Tahiti.

The light winds with the Wednesday ridge may make a good departure day
for power vessels going north, but not so good for sailing--- anyway the
incoming NW flow ahead of the Tasman Low closes this window from
Thursday 9 to Sat 11 June.

May be an OK day to sail north with the SW flow which is likely to
arrive after that Low, say on Sun 12 /Mon 13 June. BUT there may be a
deepening low in the North Tasman Sea early next week - and this may
reach NZ around Wed 15 May - that is the outlook from today's run of the
ECMWF model at http://bit.ly/ecoz .


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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