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

20 February 2012

BOBGRAM issued 20 Feb 2012

WEATHERGRAM

YOTREPS

Issued 20 Feb 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 continues to relax in the atmosphere.  Average atmospheric SOI (30day running mean) was 1.07 on 11th Feb and 0.58 on 20 Feb.

 

There is a zone of enhanced tropical convection stretching from Indian ocean (TC GIOVANA near Madagascar is part of this) across Indonesia to Philippines.  There is a counterbalancing zone of suppressed convection now over much of the Pacific Ocean. The South Pacific Convergence zone SPCZ has weakened and become disjoint since last week and is roughly from PNG to Vanuatu and across Tuvalu and Tokelau, with another branch around French Polynesia. It isn’t expected to do anything significant this week. However a LOW should form on the SZE end of the SPC Z to south of southern Cooks by Tue 21 Feb and wander off to the SE, stealing away the trade winds in that part of the tropics.  Trade winds are likely all week from Niue to Queensland and should return to Southern Cooks from Wed 22 Feb.

 

The GFS models picking that SPCZ may reactivated over Vanuatu/Fiji on weekend of 25/26 Feb, but EC model is not so keen and I’ll go with the EC on this.

 

SUBTROPICAL RIDGE STR

High that moved off to east of NZ over the weekend is expected to wander east along 42S until Wed 23 Feb and then go north and fade as a new lobe reforms at 45S.  This part of the STR looks healthy and is supporting some good trade winds in the tropics for good ‘Island hopping’ over the next week or so,

 

Next STR is in Aussie Bight and is expected to spread into northern Tasman Sea by Saturday 25 Feb. It should then extend across the South Island by Sun 26 Feb, making a cool S/SE flow for eastern NZ.

 

TASMAN SEA/NZ AREA

Low that formed crossing the EAC (east Australian current) today is expected to be well supported aloft for development as it follows the trough that i9s set for it across the South Island: 1000 near Westland on Thu, 990 to SE of Otago on Friday and 960 near 58S on Saturday. Technical name for a low that deepens 24hPa or more in 24hr is a ‘meteorological bomb’.

The southerly flow reaching NZ east coast on Sat 25 Feb as that low goes away and the next STR crosses the Tasman Sea is expected to come from 55S.  A cool change.

 

The terms used are more fully explained in the METSERVICE Yacht Pack.

           More info at http://weathergram.blogspot.com

Feedback: bobmcd@xtra.co.nz, work: bobmcdavitt@hotmail.com

 

 

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