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

29 March 2015

Bob Blog

Issued 29 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 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 switched briefly blue and positive at the start of March but has now gone
very negative again, as Tahiti drops below normal atmospheric pressure and
Darwin returns to normal pressure after recent weather.

The recent cluster of tropical cyclones may be related to a recent Madden
Julian Oscillation MJO that travelled eastwards across the South Pacific.
This can be seen as the blue/purple spread in the Outgoing Longwave
radiation anomalies observed by satellite ad graphed in this longitude-
timeline. Basically in periods of very active weather there is more cloud,
and the more white cloud there is, the lower the amount of radiation that
can escape to space / the lower (bluer) the OLR.
OLR can be seen at

This shows a yellowish-orange zone is forecast to travel east across the
South Pacific over the next week or two. This is a zone of positive OLR,
meaning less cloud than normal, and that suggests a weaker South Pacific
convergence zone.
This also shows that another MJO event is being forecast for mid to late
April that will be the last chance for cyclones in the South Pacific this
Cyclone season.

In the Northwest Pacific TC MAYSAK has formed over Palau and is expected to
travel west towards Philippines it may peel off to the north or it might
possibly make landfall around 5/6 April. Too early to tell, so be watchful.

The Cyclone that I mentioned the models were predicting to form over
Northern Cooks last Friday/Saturday never actually developed at all. AT
present it is between Niue and Southern Cooks and it does has some squally
showers, but nothing worth writing a book about.

The rain map for the last two weeks show a shift eastwards and weakening of
the strongest convective activity in the South Pacific, and a build-up of
convection in the NW pacific. Weekly rain signatures can be seen at

Panama to Galapagos
May be a good idea to wait for the onset of the next period of NE winds on
local Tuesday. If you do this then you can take a direct trip, and no need
to take the Isla Mapelo diversion. Good west going current from 2N 85W to

Galapagos to Marquesas:
Light winds at the start--- head for 5S to 6S ASAP to get into the trade
winds. Best day to depart this week could be local Monday/Wednesday
(northerly winds for starters).

SPCZ=South Pacific Convergence zone.
SPCZ is weakening away and mainly over Samoa to Southern cooks at the
beginning of the week. Another new branch may form over central Coral Sea
to Vanuatu by end of week.

STR= Sub-tropical Ridge
The STR was knocked to north of NZ during the past week, and the
northwards-knock is expected to be taken east this week as the remains of TC
REUBEN travel ESE into the mid latitudes. The low that has been over NZ
this weekend is expected to go east and fade by Wednesday UTC.
HIGH that follows that Low should travel across central Tasman Sea on
Monday/Tuesday and central/northern NZ on Wednesday/Thursday.
Next HIGH is shaped like an Easter Egg and should travel east across
Tasmania on Thursday and then across southern Tasman Sea on Friday and then
travel NE across NZ on Sat/Sun/Monday.

Over NZ
The incoming HIGH on Thursday is shovelling cold air from the southern Ocean
onto NZ ahead of it. Thus a cold front, preceded by strong NW winds and
followed by chilling southerlies, is expected to travel NE across the South
Island on Thursday and the North Island on Friday. Then clearing condition
by Saturday. In Northern NZ expect an increasing NW flow for the annual
Auckland-Tauranga yacht Race starting on Thursday, and strong and squally SW
change during Friday, and a change to easing SE winds by Saturday.
The first full moon after the equinox occurs on Sat 4 April this is the
Jewish Passover: the Sunday after it is the Christian Easter Sunday. In
AD33 the Passover Full moon was on a local Friday, this year it is on a
Saturday and there is a lunar eclipse as well visible from the Pacific (full
eclipse at 1am Sunday for Auckland). Rather strange to see the Easter moon
come and go so quickly.

The late Augie Auer would study the position and intensity and trend of all
the weather zones around the planet at the March equinox very carefully, for
he thought of this as the start of the meteorological year and that any
trends happening now will not wobble or fade, but will continue and mark the
year ahead.

Indian Ocean
You may have heard of the loss of a Catamaran (3 People on board) in the
Indian Ocean last month. A possible life-raft has now been observed at
24.317346S, 72.127445E. If you can help by spending time scanning incoming
real time hi-resolution satellite data then the Facebook page is
Many thanks

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