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

04 July 2009

BOBGRAM7 issued 5 July 2009

WEATHERGRAM
YOTREPS
Issued 05 July 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone SPCZ has been active at the northern
extend of its range between 10 and 15S especially between Papua New
Guinea and Solomons, between Tuvalu and Tokelau, and between Tuamotu and
Marquesas.

Having the SPCZ slightly further north than normal is a sign consistent
with EL NINO, and indeed the sea surface and sub-surface temperatures
near Galapagos have been on a warming trend for the past month or so and
if this continues the tropical pacific ocean will be into an El Nino
pattern by August. The Atmosphere is lagging behind the ocean, but
maybe this northern SPCZ is a sign of things to come. The Monsoon is
about a week late over inland India and delivering around 75% of its
normal rain - these sort of events are usually associated with an El
Nino, but it is not possible to jump to conclusions yet. There has been
a noticeable DROP in speed in the easterly winds between Galapagos and
Marquesas over the last week or so, and this trend is expected to
continue.

Anyway the SPCZ is, this coming week, expected to drift SOUTH in the
northeastern Coral Sea, and spread into the region between Vanuatu and
Fiji.
According to the EC model a trough or LOW may form around New Caledonia
on Friday 10 July and then wander southeastwards across the Kermadecs
area on the weekend of 11-12 July. Keep a watch on this.


SUBTROPICAL RIDGE
Weak ridge near 20S in the French Polynesian longitudes is expected to
fade away by Wednesday.

The westerly flow that dominated between Lord Howe and Kermadecs last
week is starting to ease now - this zone with have a subtropical ridge
on 7 July and then the trade winds will shift southwards.

The HIGH in the Australia Bight is expected to finally cross the Tasman
Sea on Wednesday 8 July and NZ on Thu/Fri 9/10 July. Avoid the squash
zone that will form sandwiched between the northern side of this HIGH
and that trough forming over New Caledonia (8-13 July).

TASMAN /NZ AREA
It has been unsettled over NZ lately, with occluded conditions bringing
snow to the south and cold pools bringing thundery showers to the north.

Forecast maps have one more trough/Low to cross the northern areas on or
around early Wednesday followed by a final burst of southerly showers,
and then that should be the end of this period of unsettled weather, and
the start of a period of settled weather lasting into the first weekend
of the School holidays (ENJOY) but there may be lingering southerly cold
rain/snow on the Gisborne mountains on Thursday/Friday.

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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