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

28 November 2009

BOBGRAM6 issued 29 Nov 2009

Issued 29 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 NIDA spend last week wandering off to the north of Yap

There is an equatorial westerly burst today 29 Nov and this is likely to
make another tropical low over Micronesia area during the week-but is
NOT expected to reach Nauru/Kiribati. The Low should deepen as it moves
north and may reach Guam area by around 9 Dec.

Another equatorial westerly burst in expected just north of Papua New
Guinea/Solomons from 9 to 12 Dec.

The South Pacific Convergence zone stretches from the Northern Coral
Sea/ northern Vanuatu area to around Tokelau/ Samoa and then
southeastwards to between southern Cooks and French Polynesia. The
section around Southern cooks is likely to get more active from Thu 3
Dec UTC. Vaguely related to the SPCZ, a LOW is expected to form near
25S 130W around Thu 3 Dec UTC ... something for Pitcairn's to be aware

A good sized high is dominating the subtropical ridge along 30S from 180
to 140W at present and this has enhanced trade winds on its northern
side. This high is expected to fade by Thu 3 Dec, allowing a trough to
spread east. Following this trough there is expected to be a new high
spreading east of NZ along 40S, thus taking the subtropical ridge
southwards this week.

The subtropical ridge is shifting south this week making a pattern
change in NZ away from the El Nino southwest outbreaks of the past

So this week is different: a trough with several little lows is
expected to cross central NZ on Monday, Tuesday, and Wednesday 30 Nov-2
Dec. The key to the pattern change is the High that is expected to zip
across the south Tasman Sea on Tuesday and Wednesday 1-2 Dec and then
expand east of NZ along 40S on Thursday Friday 3-4 Dec. As this High
bubs east the remains of that moist trough are expected to fade over the
North Island - so that by the weekend 5-6 Dec a moist humid northerly
flow should encompass NZ for a few days. This is a good way to start the
calendar months of summer.

A brief SW change is expected over Northland around Mon 7 Dec, but
generally this new pattern enables some good voyaging form Tonga and
Fiji to NZ for anyone still looking.

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