Bob Blog 7 April

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 7 April 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/xT9TJdZYcwE

March was a quiet month in the South Pacific tropics. There was a
brief MJO in the middle of the month which rejiggered cyclone NEVILLE
off NW Australia and MEGAN which peaked in western Gulf of
Carpentaria.


The SST pattern shows more yellow/red than blue when looking at
anomalies using the 30yer ending 2020 as the base. That, in itself,
shows global warming. Regionally, there is some cool waters showing
off the Galapagos, a sign of the beginning of a swing from El Nino to
La Nina. Also. the sea around NZ is returning to about normal and
there is a swath of below normal around 20S across the South Pacific.

Average isobars for past month (below)

During March the subtropical ridges in both hemispheres were well
marked.

The anomaly pressure pattern for March shows high pressured over Aus
Bight ad Tasman Sea , and low pressures east of NZ, thus a
predominance of SW winds over NZ. It was still through to SE of Tahiti
but the remainder of SPCZ was around normal.

Last month

The 1015 isobar has shifted north over Australia from 37S to 30S
,showing the seasonal shift in the subtropical ridge.
The Antarctic high has increased from 1010 to 1030 so the isobars are
squeezed closer together around 50S.

TROPICS
Cyclone Gamane killed at least 18 people in Madagascar and triggered
severe flooding that partially submerged villages on March 27.
OLGA is moving SW off the NW Australian coast.

WEATHER ZONES
The South Pacific Convergence zone is being rebuilt in the Coral Sea.
And has an active branch between Tonga and Tahiti. A tropical low L1
is likely to form on this branch late this week and travel south.

HIGHS and LOWS
HIGH H1 near Chatham Islands is expected to drift slowly east along
40S and reach a peak of 1036 on Thursday. It should have a squash zone
of enhanced easterly winds on its northern side between 20 and 25S
with swells over 3m. Avoid.

There is a trough off NSW (it brought flooding around Sydney on
Friday). It is expected to develop a low L2 near 160E on Tuesday. The
trough is preceded by strong NE to NW winds over NZ on Tuesday and
Wednesday, may be accompanied by rain on Thursday and Friday, and
followed by southerlies on Friday night and Saturday. Avoid.

HIGH H2 is moving in from the west along 40S and expected to reach
central Tasman Sea by Saturday.

Panama to Marquesas:
Avoid departing on Tuesday as it may be squally. Then Wednesday and
Thursday may only have light wind. From Friday a period of goo looking
northerly winds is expected to last to around Sat 20 April, good to
go, but showery from 7N to 5N.

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If you would like more details about your voyage, then check
metbob.com to see what I offer.
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Weathergram archive (with translator) is at
weathergram.blogspot.co.nz.
Contact is bob@metbob.com or text 64277762212.
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