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

25 December 2010

BOBGRAM6 issued 26 Dec 2010

Issued 26 December 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.

La NINA is still strong. Average atmospheric SOI over past 30 days is
2.3 (an increase of 0.15 in the past week). Oceanic Nino Index for
Sep-Oct-Nov is -1.4

South Pacific Convergence Zone SPCZ is in its normal location for this
time of the year, stretching across the Solomons to east of Vanuatu,
moving north and south over the Fiji/Samoa/Tonga area, then weak between
the Northern and Southern Cooks, and then reasonably active again along
south end of French Polynesia.

A Madden Julian Oscillation MJO of extra convection is appearing over
the Coral sea ... it has already activated things as shown by the brief
appearance of TC TASHA that got to gale force before making landfall
near Cairns on Christmas Eve and then fragmenting inland over Queensland
on Christmas day. Models are producing differing scenarios for where
the next cyclone may form - and maybe not much is likely to happen this
week, except for a tropical low possibly forming near Northern cooks
around Fri 31 Dec and heading for Southern Cooks around sat 1 Jan UTC.
However the chances of formation of a low in the Coral sea are
increasing and GFS is currently producing something there by 4Jan -
EC is as well, but not so intense.

Subtropical jet is conveying the moisture fields from Queensland to NZ
when it gets a chance - when frontal zones allow this --- as is expected
on Mon/Tues 27/28 Dec. Avoid.

High crossing Tasman Sea and central NZ on Tue/wed 28/29 dec, and next
one is likely from Fri 31 dec to Mon/Tue 3/4 Jan, followed by a strong
northerly flow

Front crossing NZ tonight and Mon/early Tues 27/28 Dec is being assisted
by sub-tropical jet. Avoid.

Next trough, on late wed/thu 29/30 Dec, may have separate parts - one
over southern South Island and t'other over northern North island and
should just be a transitional trough between highs.

The terms used are more fully explained in the METSERVICE Yacht Pack.
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