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

29 December 2013

BOBGRAM issued 29 Dec

WEATHERGRAM
YOTREPS
Issued 29 December 2013
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 dropped recently and is now hovering around zero. Its 30-day running mean was
minus 0.02 on 29 Dec.

MADDEN JULIAN OSCILLATION MJO
The MJO is the name given to a detectable pattern of increased convection ion the tropics
that travels from the Indian Ocean to the Pacific Ocean.
See http://en.wikipedia.org/wiki/Madden%E2%80%93Julian_oscillation
Its arrival in the western Pacific is associated with Tropical cyclone formation. The
amount of tropical convection can be traced by measurements (from satellite) of the
Outgoing Longwave Radiation OLR. Latest pattern in the OLR seems to show a quietening of
the convection in the South Pacific AFTER A possible burst of activity mid this week
around Fiji/Samoa/Tonga

TROPICAL TOPICS-
Tropical Storm SIX is to the NE of Madagascar moving to the south, and Tropical Storm
CHRISTINE is near the NW coast of Australia and expected to travel S and SE taking rain
into the interior of Australia /reducing the recent heat wave in Western Australia.
In the recent past some models were picking a possible tropical LOW to develop over Fiji
by 1 Jan. However, the convection in the Coral Sea has dried out over the weekend and the
current expectations are this development nay be delayed until 8 January (GFS model)-or
may occur south of Tonga/Niue near 25S (ECWMF model) . Things are in flux so keep watching
the local daily updates.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ seems to have dried out over the Coral Sea recently and is in a northern position
over Tuvalu and Tokelau with a weaker zone over Samoa and Tonga. It is expected to
activate over Samoa/ Tonga/ Niue by 1 January.

Sub-tropical Ridge STR
The blocked HIGH that is near 40S to south of French Polynesia and should stay put this
week. Another High is expected to move into the Australian Bight, but will now have to
wait until after 4 Jan as the remains of CHRISTINE work their way out to the ESE. This
leaves the Tasman Sea and NZ in a troughy area, between anticyclones, this week.

Tasman Sea /New Zealand
Troughy. The front that knocked 5 yachts out of the Sydney-Hobart race is expected to
cross NZ on Mon followed by a weakening trough on Wednesday and then another active
front/low on Fri/Sat, and then, early next week, the remains of TC CHRISTINE combined with
another Low from the Southern Ocean.
There may be the odd day here and there worthy for fishing, sailing, swimming, especially
in the north, but it does not look like there will be any extended period of settled
weather this week for holidaying.

However, please let me give you an you a not-so-familiar verse to the familiar refrain for
the New Year

We two have paddled in the stream,
from morning sun till dine;
But seas between us broad have roared
since auld lang syne.

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

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