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

10 July 2011

BOBGRAM7 issued 10 July 2011

WEATHERGRAM
YOTREPS
Issued 10 July 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
Southern Oscillation Index SOI remains in neutral territory: 0.08 on 3
July and 0.03 on 8 July.

Galapagos to Marquesas: The seas around Galapagos are slightly warmer
than normal and the winds there are now southerly 5 to 15knots. So the
optimum route is to head due west across these southerlies to 95W and
then head for a waypoint near 6S 134W.

South Pacific Convergence Zone SPCZ is active from northern Coral Sea
(near Solomons) to Vanuatu and then weakly active to the Fiji Area. The
part near the Solomons is expected to wander southwards into Coral Sea
this week.
There are strong SE winds over northern Queensland - associated with the
SPCZ and the high pressures stuck this week over central Australia.
There is a minor branch of the SPCZ coming and going from Tuvalu to
French Polynesia. This zone extends a trough to the southeast into the
mid-latitudes and a LOW is expected to form within this trough between
30S and 35S near 135W on Monday UTC.

SUBTROPICAL RIDGE STR
The High that is southeast of French Polynesia today, 10 July, has a
zone of enhanced trade winds on its northern side, but is now moving off
to the east and fading away.
There is a very weak Sub-tropical ridge along 25S across the South
pacific this week- typical of mid winter.
The next high is expected to stay over central Australia until Fri 15
July and cross the Tasman Sea on the 16/17 weekend and then hang around
central NZ during next week.

TASMAN SEA/NZ AREA
The disturbed westerly flow which arrived here last week is set to stay
for next few days. Between the 1020 isobar of the subtropical ridge and
the 960 isobar near 50S there are 80hPa and westerly gradient across the
area-so the embedded squall lines continue to be thundery - and snowy in
the SW mountains.
There is a SW storm near Tasmania tonight 10 July, and this should move
onto southern NZ on Wed 13 and remainder of NZ on Thu/Fri. There may
then be that new High in the Tasman Sea and a deepening low near (or
east of) Chatham Islands, with an eggbeater of a S or SW flow inbetween
harassing eastern coasts of NZ.
Heavy SW swell is likely in Tasman Sea until 14 July - avoid.

SAILING TO/FROM NORTHERN NZ.
Departing from Northland - wait a while: westerlies may be strong at
times until Thursday 14 July. Conditions should turn SW on Friday 15
July with barometer rising above 1012, and that may be OK for a
departure... but check again nearer that time as there may be a problem
low developing between Northland and Tonga next week.
The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

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