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

25 April 2010

BOBGRAM7 issued 25 April 2010

WEATHERGRAM
YOTREPS
Issued 24 April 2010
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.

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 110W,
and enjoy a following current and light southerly winds. Do not go any
further north than around 30 minutes north... After 110W head direct for
Nuku Hiva, the entry port for Marquesas, and winds should obliging
increase to 15 to 20 knots from the southeast, with settled weather.

TROPICS
Tropical Cyclone SEAN formed over the seas northwest of Australia in the
past few days, and I'm thinking it is likely to be the last of the
season, so sailors can now start to heed those tropical sirens.

South Pacific Convergence zone SPCZ has been active from Coral Sea
eastwards across New Caledonia / southern Vanuatu to Fiji to Tonga to
Southern Cooks. There has been some surface flooding around Fiji and
Tonga, and there is a burst of convection over Fiji tonight as a Low
forms in the SPCZ trough. - This LOW is expected to move southeast over
the Lau group on Monday 26 April then slowly east along the SPCZ between
20 and 23S and be south of the Southern Cooks next weekend 1-2 May.

SUBTROPICAL RIDGE: STR
HIGH cell east of New Zealand is stalled until Tuesday and will then be
reinforced and move east along 35 to 40 South to be well south of French
Polynesia for the 1-2 May weekend. There is a squash zone of enhanced
trade winds on the north side of this system around about 25S, just
south of the SPCZ. Avoid.

Next HIGH in the STR is expected to cross inland Australia rather than
the Aussie Bight. The longer nights are helping make colder denser air
over inland Australia and this high is likely to move from South
Australia on Tuesday 27 April to New South Wales on the 1-2 May weekend
to northern North Island on 4-5 May. This High will push trade winds
into the Coral Sea knocking the SPCZ to Solomon Islands / Tuvalu.

TASMAN/NZ
Low in Tasman Sea should intensify as it wanders off to the south on Mon
26 April. Associated front should reach the North Island by Tuesday and
stall between Northland and East Coast from then til Thursday bringing
some welcome rain.

Usually around this time of year there is a cold SW change that whooshes
across NZ and makes cruising sailors shiver, up-anchor and head for
warmer climes. This is similar to a front that swoops across California
in October, called the Californian flush. Well, it isn't expect to be
very dramatic, but a deep Southern Ocean Low is expected to pass
eastwards to south of Tasmania on 27-28 April and south of NZ on 29-30
April and its associated front should bring a chilly SW/S change to the
South Island on Friday 30 April and North Island on Sat 1 May. So it
should be OK to depart NZ on 2 May.

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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