Bob Blog

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 25 February 2024

Panama to Marquesas -seasonal challenges
Normally the International Convergence zone ITCZ meanders across the
Pacific Ocean in a latitude band between 10 and 2 degrees north of the
equator.
An interesting "mirror" of the ITCZ forms in the eastern Pacific at
this time of the year:
This is triggered by the overhead sun. During late February and early
March, the latitude of the overhead sun shifts slowly northwards from
11S (20Feb) towards the equator (21 Mar/equinox) and then Panama (10
April) (see table of solar declination)

This triggers a convergence zone to southwest of the Galapagos which
lingers there maybe until April, then disappears until the following
year. I call this the mirror convergence zone as it seems to somehow
mirror what is happening in the ITCZ to the north. That could be due
to the way the atmospheric currents turnover with zones of two
castling clouds sharing the same moat of sinking air.

This will become one of the challenges for vessels sailing between
Panama and Marquesas. Another challenge is that as the season changes
the southerly winds in the southern hemisphere will shift north, and
NE winds in the Panama gulf will gradually fade by early April when
the overhead sun gets north of Panama. The swells between Panama and
Galapagos become a confused amalgam but with an increasing SW
component.

One feature that is useful for sailors entering the Pacific from
Panama is the sea surface current.
I know we still have an EL NINO episode, but this is fading. EL NINO
is associated with a weaking of the equatorial west-going current, but
at present this current is looking very healthy. These currents are
taking the warmer-than-normal sea surface that EL NINO built up near
Galapagos out into the rest of the Pacific.

TROPICS

l Cyclone Potential

Northwestern Australia was drenched by slowly moving Tropical Storm
Lincoln. The storm strengthened after moving out to sea again, and
then made landfall on the far northwest coast. Tropical Storm Eleanor
looped around the Indian Ocean islands of Mauritius and Réunion. There
is still a potential for development over Vanuatu but this is
decreasing.

WEATHER ZONES
The South Pacific Convergence zone remains well established from
Vanuatu to Low L3 which is expected to travel off to the southeast.
There is another convergence zone over Northern Cooks, and tropical
low L2 south of Southern Cooks that should linger until mid-week then
fade.
There is also a convergence zone lingering south of Tahiti.

HIGHS and LOWS
HIGH H1 continues to linger well east of NZ.
Low L3 formed northwest of Auckland today, disrupting an Australian
/NZ cricket game. It is expected to deepen further as it moves
southeast, crossing Chathams mid-week. It should leave a southerly
flow over NZ until Wednesday.
HIGH H2 in Australia Bight should cross Tasmania on Monday and then
move northeast across the Tasman Sea reaching 30S to north of NZ by
Friday, followed by a trough over NZ this weekend.

Panama to Marquesas: the Northerly winds in the gulf should last all
week. Scattered squalls between 5N and 2N.

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