Bobgram 1 Dec

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.
Compiled Sunday 1 December 2024

A review of last month's weather

Here is a link to a YouTube clip giving an animated loop of the
isobars and streamlines in the South Pacific for the last month at
youtu.be/O1igNpEvKxs

November was dominated by large HIGHS travelling east across the South
Pacific. Some going around northern NZ maintaining a zone of light
winds near 30south, and some going around southern or central NZ.
Between the Highs there were troughs, with cloud bands that lingered
in a frontal graveyard near 20 to 30 South.

Over Australia front often acted like an atmospheric river taking
moisture from far north to central areas.

The Kuroshio current continues to feed warm seas across the North
pacific,

And the weaker cool tongue along the Pacific equator is a sign that
the incoming La Nina.

Average isobars for past month are at
www.psl.noaa.gov/map/images/fnl/slp_30b.fnl.html

The subtropical ridge in the Southern hemisphere has strengthened and
shifted south.
An interesting hollow of low pressure is sitting over the
warmer-than-normal waters around the Aleutian Islands in the North
pacific.

The anomaly pressure pattern for November shows the dominant HIGH over
NZ.
North America has become a breeding ground for lows.
Locally, The northern 1015 line is drifting south across Australia.
The 1020 isobar has expanded.

TROPICS
FENGAL formed over the Bay of Bengal near Sri Lanka and is bringing
locally heavy rain and strong winds to India's Tamil Nadu and Andhra
Pradesh states. EROBYN is in south-central Indian Ocean

WEATHER ZONES
The wind accumulation shows the light wind zone along 30 to 35S for
the subtropical ridge. North of that are the trade winds, with a
squash zone near 20 to 25S south of Fiji and Tonga associated with a
small low L1. South of the subtropical ridge are the strong winds of
the disturbed westerlies.

The South Pacific Convergence zone extends from Solomons to Samoa to
northern Cooks. Associated convergence zones extends from New
Caledonia to Fiji across part of Tonga to Niue and then off to the
southeast.

The MJO is moving across the Indian Ocean this week, and that means
the SPCZ should remain quiet this week. However, it is likely to
activate between mid and late December.

HIGHS and LOWS

HIGH H1 east of NZ is moving off to the east

Tropical trough/low L1 id expected to form south of Fiji on Monday and
travel slowly southwest on Wednesday and then to the southeast and
fade. There is a zone off light winds on the north side of L1.

Low L2 is crossing Tasmania on Tuesday and NZ on Thursday and Friday,
followed by H2.

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