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

07 January 2012

BOBGRAM issued 8 Jan

WEATHERGRAM
YOTREPS
Issued 8 January 2012
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.

La Nina's indicators in the atmosphere are moderating. The Southern Oscillation Index SOI (30day running mean) increased to around 2.3 when Cyclone GRANT was around and has dropped to 1.79 on Sat 7th Jan.

Recently a MJO cycle of enhanced convection was apparent over northern Australia but this as weakened away.

The South pacific Convergence Zone SPCZ is solid in an active line from Solomons to northern Fiji to central Tonga to Southern Cooks. Lows have formed between Tonga and Niue and near Southern Cooks. The low near is likely to remain much the same and slowly travel southeast.

The Low between Tonga and Niue has a moderate chance of deepening into a cyclone over next few days and may go east then get knocked to the west for a while. Watch and avoid.

SUBTROPICAL RIDGE STR
Big Fat high at 40S to well-east of NZ is a blocking high at present, so that features around it are sometimes being deflected counter-clockwise. It may shift south to 25S by Tuesday 10th and should slowly relax off to the east from around Friday 13th.

High in Aussie Bight should cross Tasmania on Sat 14th and move into Tasman Sea and ridge over central NZ during 14/15 Weekend, bringing them some welcome sunshine.

TASMAN SEA/NZ AREA
Because of the blocking high out-east, there are a few more Tasman troughs this week.
The low near Bay of Plenty is expected to be pushed westwards across Auckland tonight and then fade as it goes south across the South Island by Tuesday. After a break, a weak trough should cross the country on Wednesday and then the remains of a Tasman Low on Thursday--- bringing some welcome rain to southern areas. This should be followed by a showery SW change on Friday, and then there is likely to be a sunny high for many areas during the 14/15 weekend.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to home: bobmcd@xtra.co.nz, work: bob.mcdavitt@metservice.com

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