Issued 19 January 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 of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.
SOI 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.
SOI has bounced back up in the past few weeks. Its 30-day running mean was
plus 0.64 on 19 Jan.
Weather Pattern for the past month.
The pressure anomaly map for the past month reveals that NZ has been troughy
and most of Australia has had higher than normal air pressures.
Tropical cyclone JUNE lost energy when it encountered the tall mountain
ranges of New Caledonia and is now moving over cooler seas and slowly
winding down, and will likely be just a Low by Monday (can be called Ex TC
JUNE). It still has plenty of wind and rain near its centre and is expected
to cross North Island on Monday (= Monday night/Tuesday local time).
South Pacific Convergence Zone SPCZ
TC JUNE was the product of a burst of convective activity over the Coral Sea
early last week.
The SPCZ is now an extension of and connected to the monsoonal heat trough
over Australia. This is expected to shift north across Australia this week,
relieving the heat over Victoria and New South Wales. When this zone gets
far enough north this may help trigger the formation of a tropical low over
northern Australia by the weekend.
There is a large Low over Western Australia for much of the week, and this
is expected to drift north as well.
Sub-tropical Ridge STR
The STR is in its typical summer position across the Southern Bight and the
Tasman Sea, and along 30 to 40S well east of NZ, but remains weak around NZ.
The HIGH which is expected to bud off Tasmanian on Wednesday should cross
central NZ on Friday/ Saturday 24/25 Jan, followed by a trough heralded by a
strong NW flow on Sunday.
Tasman Sea /New Zealand
Troughy. The remains of TC JUNE are expected on Monday (night local time to
If it arrived a few days later then it could have coincided with the arrival
of a low with cold air fresh from the southern ocean ---and the combination
may have been a monster. As it is, that low fresh from the southern ocean is
expected to sideswipe southern NZ on local Wednesday night/Thursday, and by
then Ex-JUNE is likely to be near 50S.
See my yotpak at boatbooks.co.nz/weather.html for terms used.
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Bob McDavitt's ideas for sailing weather around the South pacific
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