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

20 March 2011

BOBGRAM7 issued 21 March 2011

WEATHERGRAM

YOTREPS

Issued 21 March 2011

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.

 

I didn't get time to issue a regular weathergram yesterday == I was driving back to Auckland after attending Central District Fieldays over the past week. So here it is a day later than normal….

 

TROPICS

La NINA is still strong, and weakening. The Southern Oscillation Index 30day running mean moved from 2.17 on 11 March to 1.95 on 20 March.

 

There have been some signs of extra convection off the eastern sea-board if Australia, as we expect when a MJO moves into the Coral Sea --- Sydney had a downpour, for example.  However, nothing organised has appeared so far, and current thinking is that nothing is likely to become organised in the Coral Sea over the next week or so we seem to be in a holding pattern at this stage.

 

South Pacific Convergence Zone SPCZ is loosely draped from Solomons to Fiji and around Southern Cooks and French Polynesia.

 

SUBTROPICAL RIDGE:

HIGH 1 is typical of a La Nina summer high – wondering off to east of South Island along 45S and then heading NE to around 30S east of 160W.

 

HIGH 2 is actually one from the sub-polar regions,  today 21 March/Equinox it is at 50 to 55S to south of Tasmania.  It should wander to east of South Island on Wed 23 March, (World Meteorological day), preceded by a cold southerly, and then go east along 45S from Thu 24 to Sun 27 March, followed by a broad northerly flow.

 

HIGH 3 is expected to take a more northern route – crossing New South Wales on Mon 28 March and North Island on 1-2 April.  A sign that we are now in the equinoctial time of the year, and the roaring 40s are generally heading north.

 

There are useful trade winds on the northern side of all these Highs.

 

NZ Area

 

A sub-tropical low formed on the western shoulder of HIGH 1 and tonight / Tuesday is moving SE and sideswiping the NE of North Island.  It may deepen to below 1000 when east of southern Hawke’s Bay, bringing them wind and rain after a long dry spell - a good chance, too, for Wairarapa and maybe for Marlborough to have an autumn flush, a last chance for some grass growth.

 

A large sub polar low is expected to follow HIGH 2, with a minor front crossing NZ over the weekend - preceded by a strong N to NW flow on Friday/Sat 25/26 March and followed by disturbed windy and showery W/SW flow on Sunday 27 to Wed 30 March – something more like winter is on its way.

 

SO it may be an idea to avoid North Island/ Tasman Sea this week

           - Weather pattern here should settle by mid next week.

 

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

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

             Feedback to bob.mcdavitt@metservice.com

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