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

07 August 2010

BOBGRAM7 issued 8 Aug 2010

WEATHERGRAM
YOTREPS
Issued 8 August 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.

TROPICS
More heavy rain is forecast in the Monsoon over Pakistan this week, and
lots of rain over much of Indonesia. A conveyor belt directed some
moisture from there to NZ over the past few days. If you have access to
Internet see this at http://www.ssec.wisc.edu/data/comp/wv/wvmoll.mpg

The South Pacific Convergence zone SPCZ is strong about the Solomons and
somewhat quiet elsewhere. It is expected this week to build in the
Tuvalu and Tokelau area, and this may spread towards Samoa by the end of
the week.

Passing troughs in the mid-latitudes are extending far enough northwards
to affect the southern parts of the tropical South pacific, but not to
reach the SPCZ. One of these is located south of Fiji tonight and
should wander east and reach Southern Cooks by Thu 12 Aug UTC...
Preceded by a swing of the trade winds so they come from the NE,
accompanied by some squally rain, and followed by southerly winds and
clearing weather. Another of these troughs is expected to form off the
east coast of Queensland on Tue 10 Aug and wander east across the Coral
Sea to reach New Caledonia by Thu 12 Aug. If sailing, try and plan
around these troughs - at least remember that the computers and GRIB
data can not resolve the details near them.

SUBTROPICAL RIDGE: STR
Long wave pattern continues to be conducive to forming troughs in the
Tasman Sea and helping the STR in longitudes east of the dateline.

The HIGH forming now/8 Aug UTC over western Tasman Sea is expected to be
rather slow and weak until it crosses northern NZ on Wed 11 Aug and then
should expand east of NZ until Sat 14 Aug. There is likely to be a
zone of enhanced trade winds on its northern side.

TASMAN/NZ
A southerly start to the week with an outgoing low- barometers are
rising. Rain was briefly intense on Saturday and there are still some
intense showers around- in Wellington slips are disrupting traffic.

Fronts following Wednesday's high are likely to cross NZ on Thu 12 and
Fri 13 Aug, followed by a low that may linger over Northland for the
14/15 weekend.

So it is OK to sail towards Northland if you can get there by
Wednesday, and anyone planning departure should consider waiting until
next week.


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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