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

22 November 2009

BOBGRAM7 issued 22 Nov

Issued 22 November 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.

Tropical cyclone ANJA faded east of Mauritius during the past week.
The South Pacific Convergence zone stretches from the Northern Coral
Sea/ northern Vanuatu area to around Tuvalu to Tokelau and then
southeastwards between northern and southern Cooks and then across
southern islands of French Polynesia FP.

A small low is expected to form in the SPCZ around southern FP on Mon 23
Nov UTC and wander off to the south - some clockwise winds with this low
and it is likely to be followed by a wind flow from the north or
northeast over FP.

SPCZ is expected to get active this week west of the dateline, in
response to the travel of a Madden Julian Oscillation MJO from Indonesia
to the Papua New Guinea/Solomons area. SPCZ may take a trip south
towards Fiji and Tonga on the 27/28 /29 Nov weekend, according to
today's run of the NOGAPS model-bringing them some now-welcome rain.
Other models say no.

The trough which crossed NZ this weekend (dropping temperature in Timaru
from 28 to 15 C at Saturday brunch in typical Canterbury spring fashion)
is expected to help trigger a low south of southern Cooks near 30S 160W
on Mon/Tue 23/24 Nov. This Low will "steal the wind" between the Cooks
and Niue as the low itself moves off to the south from Tue 24 to
Thursday 26 Nov.

The upper atmosphere has been encouraging highs over South Australia and
Tasmania and lows around Chatham Islands. These highs have built
heat-wave conditions over South Australia. The combination of highs to
the west and lows to the east has encouraged cold southwest outbreaks
over NZ - a typical El Nino spring scenario.

This coming week is offering more of this pattern, but with a
slow-moving high that may well touch Northland.

The high in the north Tasman Sea today 22 Nov is expected to fade there
by Tuesday 24 Nov, as a front and SW flow spreads over NZ on 25 Nov,
severe in the south.

A new High is expected to squeeze along 35S from Australian Bight to
Tasman Sea on Tues 24 Nov, and then noodle northwards across the Tasman
Se on Tue to Thu 24 to 26 Nov so that it stretches west to east along
30S between NZ and Fiji from Thu 26 Nov to Mon 30 Nov. There is likely
to be a squash zone of enhanced trade winds to north of this high - in
Coral sea from 24 to 26 Nov and extending from Fiji to French Polynesia
from 26 to 30 Nov.

On Fri 27 Nov a low at 50S in the Southern Ocean may deepen as it passes
by, making for another vigorous SW blast over southern NZ.

Lows are also expected to deepen in west Tasman Sea on Fri 27 Nov and
Sat 28 Nov and cross central NZ on Sat/Sun/Mon/Tue 28/29 Nov and 1 and 2
Dec. Avoid these lows. Also these lows may trigger a change in the "SW
pattern" that has been affecting NZ over last month or so.

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