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

18 January 2015

Bob Blog

Issued 18 January 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 COMET online weather training Program is pleased to announce the
publication of "Chapter 7, Synoptic and Mesoscale Systems" as a part of the
new 2nd Edition of their online textbook, "Introduction to Tropical
Meteorology". The textbook is being developed over time and its chapters are
being re-published incrementally. Please follow this link for more
information and link to the new textbook chapter:
(no charge to register). I also recommend their omega equation module.

AT the NZ Met Society Conference in Nov 2014 there was a poster detailing
progress of the SWFDDP, the Severe Weather Forecasting and Disaster Risk
Reduction Demonstration Project around the South Pacific. Thanks to the Met
Society this poster is now on line at

If you are one of the lucky who are involved in this project then check this
poster and share with friends (if access allows). Data from this project's
website is checked as part of the data used for these Weathergrams.

The Ocean: extra heat has been stored in the Pacific Ocean for a while now
and all the Oceanic indices have crossed the threshold into El Nino

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 July and dived below -10
(Australian units) for much of September, and again for a week in November,
then relaxed in early December, and has been relaxing over last few weeks.

AT present Cyclone MEKKHALA is in the NW Pacific (weak, but it did help
bring some rain to Manila for Pope's Mass), and there are two named systems
in the India Ocean: BANSI (which formed last week and is now easing near 25S
74E) and CHEDZA (a weak system east of Madagascar). A new Tropical Low is
over the West Kimberly and may deepen into a named system on Monday UTC as
it skirts the NW Australian coast. Check for

The MJO cycle I mentioned in last week's edition showed up as extra oomph in
the South Pacific Convergence Zone that brought heavy rain to Vanuatu last
Thursday. This oomph this already cleared away from the Coral Sea and is now
over the French Polynesia area and may help develop a tropical depression in
the area by Monday UTC. This system should travel slowly south and there is
likely to be a squash zone of strong to gale easterly winds between this
system and a large HIGH near 40S. Avoid.

The Vanuatu/New Caledonia area is having a respite at present but another
tropical low may form there on Monday/Tuesday UTC. This feature is expected
to travel south and, by Friday, turn into a stationary trough located
mid-Tasman and west of North Island.

The weekly rain maps over the past fortnight show last week's burst of rain
over Vanuatu and a build up over French Polynesia. These maps also show the
recent rain about Madagascar - and inland to Mozambique and Malawi, South
Africa. Also the cyclone track of MEKKHALA in the NW Pacific.

SPCZ=South Pacific Convergence zone.
SPCZ is expected to be strong this week from Tuvalu to Northern Cooks to
French Polynesia, with another convergence zone over Fiji /Samoa and Niue
and a third over Vanuatu and New Caledonia.

STR= Sub-tropical Ridge
A large HIGH is expected to travel slowly east along around 45 to 40S well
east of NZ,
A weaker HIGH is expected to cross the southern Tasman Sea from Mon to
Wednesday and then central NZ on Thursday and then travel east along 40S,
east of NZ, from Friday onwards.

Over NZ
A trough is expected to affect the South Island on Monday and the North
Island on Tuesday and Wednesday.
On Thursday and early Friday, light winds with a passing high.
Then, from late Friday to Sunday, another trough is expected to travel
across NZ.

See my yotpak at for terms used.
Weathergram text only (and translator) is at
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