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

10 April 2021

Bob Blog 11 April

Bob Blog 11 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 11 April

Here comes the MJO again.
The MJO is a pulse of extra energy that travels around the tropics, mainly
from the Indian Ocean to the Pacific Ocean. It takes around a week or so to
pass each place and visits maybe once every 6 or so weeks. This coming week
it is going to travel across the Pacific Ocean, and may trigger some
interesting weather.
It can be seen best by looking at the MJO index 5-day running mean as seen
by the CPC Climate Prediction Centre at
This shows we have had five MJO cycles since last October (blue tracks) and
the current cycle is the quickest.
Another way of looking at the MJO is to use the Outgoing Longwave Radiation
(OLR) as a proxy. The blue lane in this diagram shows low OLR due thicker
than normal cloudiness.

The Tropics
The latest cyclone activity report is at and Tropical
Cyclone Potential is from
There is also Tropical Cyclone SEROJA in the SE Indian Ocean which is
forecast to make landfall over Western Australia on Monday. And there are
some zones of moderate to high potential risk for the formation of a
tropical cyclone in the western Pacific thanks to the passing of the MJO
this week. Just a reminder that the cyclone season in the Southern
Hemisphere nominally lasts until the end of April.

SPCZ=South Pacific Convergence zone.
There is expected to be one branch of the SPCZ in the northern Coral Sea
this week, then, in spite of the passing MJO, there is a gap around Fiji,
and then another branch between Samoa and French Polynesia s.
Low that passed over New Caledonia last night is expected to zip southeast
past the NE of NZ on Monday.
Passing trough on the SPCZ is expected to visit between Aitutaki and Tahiti
on local Monday/Tuesday, followed by SW winds for the remainder of the week.

Subtropical ridge (STR)
High is expected to travel along 30S into the central Tasman Sea on
Tue/Wed/Thu then linger rover northern NZ until the weekend. This offers a
reasonable voyage between NZ and the tropics, or from Noumea to Australia
this week, but NO GOOD for getting from Australia to Noumea.

Aussie/Tasman/NZ troughs
Low developing in south Tasman Sea on Monday is caught on the western side
of its upper trough, and thus expected to travel northeast on Tuesday
bringing with it some large swells. It should fade over the North Island on
Wednesday, followed over Thursday and Friday by a westerly flow south of

Panama to Galapagos/Marquesas
Light winds around Panama, otherwise moderate south to southwest winds
between 5N and Galapagos.
Taking the current into account, it looks better to get to Marquesas via
south of Galapagos this week.
If you would like more detail for your voyage, then check to see
what I offer.
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