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

18 March 2012

BOBGRAM issued 18 March 2012

WEATHERGRAM
YOTREPS
Issued 18 Mar 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.

A new pulse of enhanced tropical convection or MJO has been having an impact on Northern Australia during the past week with TC LUA forming off the NW coast and now moving inland, also there is a new tropical low in the Gulf of Carpentaria about to move inland, and clouds are building in the Coral Sea.

All this development has seen the isobars dropping over northern Australia, and as a consequence the Southern Oscillation Index or SOI has been going up: from 0.2 on 11 march to 0.5 on 18 March.

The South Pacific Convergence Zone SPCZ is slowly reforming in the Coral Sea area and has some bursts of activity between New Caledonia an Fiji. The main branch of the SPCZ is from Samoa to Northern Cooks to French Polynesia—somewhat east of normal. The SPCZ is mixing with a mid-latitude trough and a Low near 40S 135W but low is expected to weaken and go off to the southeast, breaking this link.

Galapagos to Marquesas: Too early for this voyage: The ITCZ International Convergence Zone has jumped across the equator and is near 5S from 170W to 90W and this makes the 'puddle jump' too squally to consider just yet. The reason for this rare jump by the ITCZ is because the sun is almost directly over the equator at present --- things should sort themselves out again after the equinox on Wednesday.

SUBTROPICAL RIDGE STR
High1 crossing the South Island tonight is expected to move off to the northeast of Chatham Islands by late Tuesday 20 March--- it may be quicker for the Volvo yachts to get south ASAP to west of Chathams rather than take the great circle that is east of Chathams. Then the High split into two… the northern part should fade away and the southern part should travel east along 45S.
Next large high is expected to enter into the Aussie Bight around Fri 23 March and, at this stage, is expected to cross Tasmania on wed 28 March—taking a track slightly further north than the last few highs.. a sign that the season is changing.

TASMAN SEA/NZ AREA
Two tropical visitors are expected this week. The first is already a low approaching southwestwards from the north so that its rain-band is expected to cross much of the North Island on Monday and Tuesday. Then another low is expected to move onto Northland and Auckland from the north on Wednesday and then go southwestwards and then south across the South Island on Thursday—these somewhat unusual tracks are being directed by a upper low.
NZ should enjoy a brief ridge on Friday 23 March—World Meteorological day- a day where weather forecasters all around the world acknowledge the official commencement of the WMO in 1950.
Then another trough is expected to cross South Island during Saturday and North Island during sat night/sun morning 24/25

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback: bobmcd@xtra.co.nz, or bobmcdavitt@hotmail.com

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