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

15 February 2015

Bob Blog

Issued 15 February 2015
Bob McDavitt's ideas for sailing around the South Pacific.

The Ocean: extra heat has been stored in the Pacific Ocean for a while now,
and Oceanic indices are still in El Nino territory but relaxing. In fact Sea
surface temperatures in the eastern Pacific Ocean are now less than normal.
But they remain above normal in the western 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,
then relaxed in early December and during January, and is now diving

The tropic are going through a quiet time at present There are some tropical
lows around NE of Australia and maybe in Gulf of Carpentaria moving south,
and one over Vanuatu and another to NW of Australia both of these are
travelling southeastwards and not expected to develop.

The weekly rain maps over the past fortnight show a shift in the most
intense rain southwards across the equator and towards NE Australia. This is
the zone with the warmest sea surface temperatures in the planet at present
and it has stored plenty of heat in the last month to feed several top
category cyclones. What has been missing over recent weeks is the
opportunity. Late this month we expect another MJO cycle of enhanced
convection to travel east across northern Australia and into the Coral Sea
so although the risk of a cyclone may be low this week, it is expected to
rise rapidly towards the end of February.

SPCZ=South Pacific Convergence zone.
SPCZ should slowly intensify this week in the Coral Sea The tropical low
near Vanuatu today is expected to travel SE to south of Fiji and be ripped
apart by the strong SE winds at the surface and strong NW winds aloft. There
is a jet stream between NZ and Fiji at present and this can help rip things
apart (it can also help develop things if they are in the right place but
more about that at another time).

STR (Sub-tropical Ridge) and over NZ
A large HIGH is travelling slowly across NZ next few days. Its eastern flank
is expected to weaken away from Tuesday to Wednesday allowing a trough and
southerly change to affect the east coast on Thursday and Friday, and then
the western flank of the HIGH is expected to travel across southern NZ on
Sat 21 and then off to the east leaving a NE flow over NZ.

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