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

08 March 2015


Issued 8 March 2015
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

First of all are any of you sailing from Australia to the islands of Papua
New Guinea or Solomons this year, especially around August/ September? If
so please read the article starting at page 36 on This tells the story
of Hans Clemmensen on SV Seagoon in Cairns who is seeking yachts to help him
get solar panels to islanders in these areas. If you would like to help
then contact him on, or read more on his websites and blog on

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean)
sums up the weather pattern over the South Pacific as one number. It is
based on the standardized difference in the barometer readings between
Tahiti and Darwin. It has been negative since last July but has risen to
take positive values in the past two weeks. Maybe this autumn will be like
last autumn?

There are two small tropical lows at present in the Indian Ocean and a weak
one near Marshall Islands, but the main tropical low worth watching is the
one that is presently named 93P or 11F, near 8S 170E , between Tuvalu and
Santa Cruz Islands.
This depression is still in the formative stage of becoming a Tropical
Cyclone and is expected to do so on Monday, and then affect Vanuatu on
Wednesday and Thursday and then go off to the SE.
This is likely to become a twin or triplet--cyclone event--- another cyclone
may form in the Coral Sea near the Australian coast by Wednesday and also
travel to SE, close to south side of New Caledonia by Monday 16th March.
And a third may briefly form off the NW Australian coast on Wednesday and
travel SW/S and fade by Saturday.
The rain map for the last week shows that the wettest area at present is in
the Kiribati/Tuvalu area, with other rain maxima near Port Hedland (NW
Australia) and on west and east side of Madagascar.
During February the averaged isobars show a zone of high pressure zone
straddling from south Indian Ocean across NZ to west of the Andes: this is
the Subtropical ridge.
Looking at the anomaly map, As seen at http://www.esrl.noaa.
gov/psd/map/images/fnl/slp_30a.fnl.anim.html, shows that during February
there was often a blocking High between the Australia Bight and NZ. This
explains the recent light winds and dry weather. This pattern is now
changing, as shown this weekend, when a front from the southern ocean was
able to cross all of NZ (albeit briefly).

SPCZ=South Pacific Convergence zone.
SPCZ is expected to intensify during the coming week between Coral Sea and
Samoa and may trigger the formation of two tropical cyclones.

STR= Sub-tropical Ridge
A rather slack High pressure area I expected to cross NZ from Monday to
The next HIGH is expected to travel from Australian bight across Tasmania on
Friday and then stall in the Tasman Sea over the weekend, nicely placed to
help divert the tropical cyclone that may then be north of NZ off to the SE.

Over NZ
Mixed weather from Monday to Wednesday with reasonably light winds but a
scattering of showers in a weak ridge.
A front is expected to cross NZ on Thursday and Friday followed by a
southerly on Saturday, and then a SE flow over northern NZ on Sunday in time
for the Volvo restart, with strong southerly winds/big southerly swells
still lingering off the NZ east coast.

See my yotpak at for terms used.
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