BOBGRAM7 issued 16 May 2010

WEATHERGRAM
YOTREPS
Issued 16 May 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 124W,
and enjoy a following current and a light southerly wind. Then head
direct for your destination and winds should obliging increase to 15
knots from the southeast or east. Weather mostly settled; some showers
around 92W and 100W. Also very showery along the Intertropical
convergence zone between 5 and 9N so don't stray that far away.

TROPICS
South Pacific Convergence zone SPCZ has been knocked around lately and
that zone of cloud and squalls stretching from off Queensland to south
of Fiji and then out to the southeast is a reflection of the subtropical
jet rather than the SPCZ.

The SPCZ is slowly reactivating around the Solomons to Tuvalu and around
Northern Cooks to French Polynesia. There is a burst of active
convection over Indonesia at present but that will take weeks to get
into the Pacific and is more likely to affect Micronesia rather than
South Pacific.

However, we should remember that squalls in that trough line south of
Fiji can still be a problem. I had an email today recording a good 35
knots of winds around 160 miles south of Suva. So keep in mind that
the GRIB files and isobars don't work 100% near troughs.

SUBTROPICAL RIDGE: STR
HIGH1 from last week continues to dominate proceedings and is 1038 at
40S 150W... should continue to wander east reaching 090W next weekend
with a touch to north to 33S where it will become the Andes High for a
while. As mentioned last week, there is a strong squash zone of the
northern side of High1--- many yachts were sheltering from it in Minerva
all last week. This squash zone is exacerbated between High 1 and a low
that has formed to southeast of French Polynesia - Fiji Met have just
issued a gale warning on this zone. The Low is blocked and is likely to
move south then southwest and fade into the next incoming trough of Tue
18 May.

Next High along the STR is barely showing itself as it crosses New
Caledonia tonight 16 May, and south of Fiji and Tonga on Tue/Wed 18 /
19 May and then should be more noticeable south of Southern cooks at
30S by 20 to 21 May.

Following High in the STR will be more to the South, rolling along 45S
to south of Tasmania on 20 May, heralded by a southerly outbreak that
may toss cold southerlies with rain then snow onto southern New Zealand
from Fri 20 to Sun 22 May.

TASMAN/NZ
Large Catherine-wheel low in the Tasman Sea is rotating clockwise
underneath its cut-off upper low and should finally cross NZ on Tue 18
May and its associated trough should reach Northland on Wed 19 May
followed by only brief SW winds.

Next trough rolls in from the southern ocean onto South Island from Fri
20 to sun 22 May, pushed in by that high in the STR, as mentioned above.

The Jet stream over Queensland looks primed to produce another Tasman
Low. Latest GFS model has this crossing the Tasman and reaching NZ
around 26 -27 May, but the latest EC model http://biy.ly/ecoz has its
warm fronts reaching NZ around 23 to 24 May, and that seems closer to
the observed recent rhythm in the STR. Those preparing for the Auckland
to Fiji race taking off on Sat 22 May will be keeping a close eye on
these models, and the http://bit.ly/7daywx model all during the coming
week.

Those of you who have email at sea can download the latest NZ high seas
forecast by sending an email to query@saildocs.com, no subject needed,
with message SEND http://bit.ly/suntropic, as well as listening to it
on ZLM.

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