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

01 March 2015

Bob Blog

WEATHERGRAM
YOTREPS
Issued 1 March 2015-a special day for any Welsh called David.

Bob McDavitt's ideas for sailing around the South Pacific.
The Ocean: During 2014 extra heat was stored in the Pacific Ocean, and
Oceanic indices were in El Nino territory for a while. This year there are
still above average SST in the western Pacific, but SST has reverted to
normal in the eastern and central Pacific.

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,
and in late January, and in the last week has relaxed to near zero.

TROPICAL TOPICS
Apparently TC MARCIA might have only spent a brief time of its life at
Category 5. The important lesson is that these small sized cyclone can pack
a (briefly) big punch, especially in March, and so we should treat them with
the utmost respect.
At present TC GLENDA is over the open sea in the Indian Ocean.
No tropical cyclones are expected in the South Pacific this week, but people
in the Solomons are at risk during next week 10-13 March.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ should slowly intensify this week in the Coral Sea.
A tropical trough mid-week over Fiji/Tonga/Niue/Southern Cooks is not
expected to come to much, but IS expected to help form a Low by the local
Wednesday south of Southern Cooks and this should then move off to the SE,
killing the winds over Southern Cooks.

NIWA have produced a map showing the expected position of the SPCZ in March
and April (green line, with white whiskers at 1 and 2 standard deviations).
(They do not tell us what the red line indicates).
see
http://www.niwa.co.nz/island-climate-update-173-february-2015/south-pacific-
convergence-zone-forecast-february-to-april-2015


STR (Sub-tropical Ridge) and over NZ
The STR is still over northern NZ, as is typical of this time of the year.

South of the STR are the roaring 40s, and the fronts in this zone are having
impact over the South Island and having increasing impact over the North
Island. One of these fronts should cross South Island and central NZ on
Monday and Tuesday. After a brief respite on Wednesday a stronger front is
expected over the South Island on Thursday and the North Island on Friday,
followed by SW/W flow over most of NZ (not the far north) on weekend of 7/8
March. The seasons are changing.

NZ farmers may talk of dry soils in parts of NZ, but the NIWA SPI graph
shows mostly average rainfall during February.
See http://www.niwa.co.nz/static/climate/last30daysspi.png?1234

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
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