Bobgram 9 March

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 9 March 2025
The March of the Sun in March
During March the latitude of the overhead sun (also known as the sun's
declination) changes from 10S to 5N. On the 21st it is over the
equator, and we call that event the equinox (10:01pm, Tuesday 20 March
NZDT).

When the overhead sun is between 10 and 5S in early March it often is
associated with the formation of a convergence zone located SW of
Galapagos. This convergence zone mimics the intensity and mirrors the
position of the Intertropical convergence zone:



This year it has produced a strong east going surface current around
the Galapagos:

This poses challenges to anyone attempting the Panama to Galapagos
voyage over the next few weeks

TROPICS
The latest cyclone activity report is at zoom.earth and
tropic.ssec.wisc.edu and Tropical Cyclone Potential is from
www.ospo.noaa.gov/products/ocean/tropical/

GARANCE got to Cat 3 near the island of Réunion killing at least 5
people.
HONDE left at least three people dead and numerous buildings wrecked
in southern Madagascar. •
ALFRED brought a storm surge and heavy rain to Brisbane, killing at
least one person.
We can see how the track of cyclone stutters by watching ALFRED
approach Brisbane…
Last Tuesday/Wednesday what date/place would you have picked for
landfall, and how wrong would you have been?

JUDE is skirting around Madagascar
IVONE is over open sea in mid-south Indian Ocean.

WEATHER ZONES
Weather Zones Mid-week GFS model showing isobars, winds, waves
(purple), rain (red), MT (Monsoonal trough), STR (Subtropical Ridge),
SPCZ (South Pacific Convergence Zone) CZ (Convergence Zone)

Rain accumulation this week from Windy.com shows The SPCZ active over
Vanuatu and Fiji. Alos there is another active convergence zone over
Samoa with flood warning.
And there is that "mirror convergence zone" at 5S to SW of Galapagos.
heavy rain from Tonga to Niue and with ALFRED.


Wind accumulation this week from Windy.com
The wind/rain accumulation shows trails of wind and rain mapped out by
L1
LOWS and HIGHS
Low L1 is expected to form (from under an upper cut off) to the NE of
northland on Monday and then travel to SE
A cold front /trough is expected to cross NZ on Monday/Tuesday
followed by a southerly flow. In this cold air a Low is expected to
form neat Chatham Island by late Thursday and then move off to the
east.
HIGH H1 south of Tasmania on Monday is expected to be diverted so that
is travels slowly north across the Tasman Sea this week. It should
push a ridge over southern and central NZ on Thursday and then weaken
into a ridge over Northland by end o week.

ALFRED is moving slowly south and MIGHT go inland late in the week
near Brisbane.
HIGH H1 now over North Island is moving off to the ESE.
This allows an active cold front to travel NE over NZ on Monday and
Tuesday and then form a Low L2 near Chathams on Wednesday with a
strong SE flow over NZ.
That should be followed by H2 now in Australian Bight and travelling
east across South Tasman mid-week then onto Northland for the weekend.

Low L2 in Australian Bight is expected to travel SE. Associated FRONT
is expected to travel east and cross NZ on Friday and Saturday
followed by a westerly with some strong winds.
HIGH H2 in Aussies bight is expected to be diverted to north of Hobart
and then northward to merge with H1.
Gulf of Panama: A useful NE flow for starters
Galapagos: There is a "mirror" CONVERGENCE ZONE with squalls a about
and mainly to SW of the group. Strong East to SE flowing surface
current around the group this week.
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If you would like more details about your voyage, check metbob.com
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weathergram.blogspot.co.nz.
Contact is bob@metbob.com or text 64277762212.
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