BOBGRAM issued 8 Dec 2013

WEATHERGRAM
YOTREPS
Issued 08 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.

Last week I commented how the International Research Institute of Columbia University have looked at the plume of 24 ENSO models and shown that the probability of an El Nino event MAY increase to over 50% by mid-2014. I should reiterate that at present there are no signs that this is actually happening yet.
However, the term El Nino comes from the festival of El Nino de Navidad (Christmas) – and gets this naming because this climate variation often starts out with the arrival of warmer than normal sea along the Peru Coast during December. There does indeed seem to be some warmer sea along the Peru Coast at present—but cooler sea around Galapagos, so we have something like a mixed bag at present.

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 is currently on a rising trend and its 30-day running mean reached 0.7 on 8 Dec. So the current trend is towards the La Nina side of things.

TROPICAL TOPICS
TC MADI is travelling north towards the east coast of India , so the Northern hemisphere cyclone is still open.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is now returning to its normal position and is expected to visit Fiji and Tonga on Monday/Tuesday/Wednesday this week. Another branch of the SPCZ should remain slow moving over Samoa/Tokelau to Northern Cooks.
A Monsoonal trough or heat trough is forming over northern and NE Australia this week and is expected to cause strong northerlies along the east coast on Monday and Tuesday. The low that is expected to bud off the eastern seaboard of Australia on Wednesday should reach NZ on Thursday as a trough.

Sub-tropical Ridge STR
The STR is now returning to a more normal latitude of 30S in the South Pacific, but is constrained to its summer position of the Australian Bight by the heat trough over Australia.
Another High is likely to move northeastwards from the south and east of NZ starting Tuesday 10 Dec and continuing across the South Pacific, getting to 40S south of French Polynesia by Tuesday 17 December.

Tasman Sea /New Zealand
Low is expected to move away from southern NZ on Monday, followed by light winds over the North Island.
Next trough is expected to be intense over the South Island on Thursday and less intense over the North Island on Friday 13th, followed by a period of S/SW winds.
A weaker trough is expected to cross NZ on Sunday 15 December followed by a HIGH over the central and southern parts (E or SE winds for Northland).

See my yotpak at boatbooks.co.nz/weather.html for terms used.
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