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

05 October 2014


Issued 5 October 2014
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

8 October eclipse
Many of you will be watching the full moon rise with the setting sun on
Wednesday evening. And there is a lunar eclipse this month as well, so that
a few hours after moon rise you can watch it get shaded by earths shadow.
Eclipse starts at 0817UTC and finishes at 1332UTC, should be compelling
viewing if local clouds keep away .
This eclipse reminds me that when the full tide is in the middle of the
night after the October full moon (and thats around 15 Oct this year) there
may be a spawning of the Palolo coral warm. They drop off their worm-tails
or pods; jade (female) or brown (male), and these mix together in the
swirling tide, with each having a light sensitive spot that directs it
towards the moon (then sinking in the west) or a flashlight.
At dawn the pods dissolve, allowing eggs and sperm to get together and form
the new generation. The rising is only on the turn of that one tide and only
takes place for a few hours. Actual timing varies each year, and may be in
November rather than October.

This is worm-sex, Pacific style. The pods can accumulate in the sea in
massive amounts. Ask the locals about this and if you time it right you may
be about to collect some of this rare delicacy, or photo it. They might look
yucky, but taste really nice on toast, something like caviar, so Im told.

Background influences
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 standardised difference in the barometer readings between
Tahiti and Darwin.
It has been negative since July and dived below -10 (Australian units) for
much of September, but is slightly relaxing so far in October.
The amount of heat that is being stored in the sea in the Eastern Equatorial
Pacific has also increased, as measured by the NINO3.4index.
The atmosphere and ocean are in cahoots.

At this time of the year, with the sun directly overhead the 5 to 10S zone ,
we need to be mindful of a phenomenon called Cyclone twinning whereby a
cyclone forming near 5 to 10N in the northern hemisphere seems to influence
the formation a feature of similar size and shape in the southern
hemisphere. This happens reasonably often in the Indian Ocean (see
) and was maybe a factor in
the formation of the infamous cyclone Bebe in the South Pacific in 1972.
There is possibly some twinning occurring with features around 10N and
10S at presentbut no cyclone twinning. Westerly winds near the
equator can be part and parcel of low pressure systems at both 10N and 10S.
And a streamline analysis (from MetService) shows equatorial S/SW winds to
north of Papua New Guinea.
As for Tropical cyclone activity at present we have TC PHANFONE and VONGFONG
in the NW Pacific, and SIMON off the Mexican west coast.
The weekly rain maps show the heaviest rain around 140E and part of it over
western Solomon Islands.

SPCZ=South Pacific Convergence zone.
SPCZ is expected to be active in the zone from Solomon Island across the
Coral Sea to New Caledonia between now and Tuesday, extending across Loyalty
Islands to south of western Fiji on Wednesday and Thursday, easing away on
Friday. There is also a weak convergence zone from northern Tonga to
Southern Cooks and an active trough that is expected to lurk around 140W to
south of 20S from Tuesday until Friday

STR= Sub-tropical Ridge
The High travelling east along 30S from Australia is expected to bring a
brief period of light winds to NZ on Tuesday. The next high is expected to
be in the Australian bight on Wednesday a more summer-like latitude.
This high is expected to travel east along 30/35 across the Tasman Sea on
Thursday/Friday and northern NZ on Sat/Sunday. This provides a very good
weather pattern for anyone wishing to sail southward towards NZ.

Departing westwards from Tahiti:
With just that weak convergence zone to contend with the weather pattern is
looking reasonable for westward travel. Note that towards the end of the
week, a high cell is expected to travel east along 30S - and there is likely
to be a zone of enhanced SE trade winds on its northern side, especially
along 20S.

Between the tropics and NZ
With the prospect of a high crossing northern New Zealand next weekend, this
implies and good weather pattern for setting sail to NZ over next few days.
However a departure from Tonga /Fiji/ on Monday to Wednesday or from Noumea
on Monday/Tuesday, is likely to start off with strong SE winds.
SO it is a mixed week.
Note that fronts with squall winds are expected to affect North Island on
Monday and Wednesday.

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