Issued 2 Dec 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.

The Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) had a value of MINUS 1.01 back on 25 Aug. It has been gradually rising ever since and on 02 Dec was plus 0.4. Computer models are picking a neutral SOI for the cyclone season.

Tropical cyclones: Last week TC BOLDWIN was in the Indian Ocean. This week TC BOPHA is in the NW Pacific heading for the Philippines.

South Pacific Convergence Zone SPCZ

The South Pacific Convergence Zone SPCZ has stayed much the same in the past week between Solomons, Vanuatu and Fiji with a side branch from Tuvalu to Tokelau to Northern cooks. At this stage not such change is expected in the SPCZ during the coming week.


The STR has been reasonably strong between 25 and 30S across the South Pacific during the past week and is expected to divide into High cells that may take a more southern route this week.

One cell stretched from 170E to 140W along 25 to 30S tonight and is expected to fade away by Tuesday, leaving behind a high near 35S to east of NZ. This high is expected to move east and intensify to a central pressure near 1020 near 150W by Saturday 8 Dec, with a squash zone of intensified trade winds over Southern Cooks.

Next high is expected to move off new South Wales into the central Tasman Sea on Thu/Fri/Sat 6/7/8 and then across central NZ on Sun/Mon to be mainly east of the South island at 40S by Tuesday 11 Dec. The following High may cross Tasmania on Tue/Wed 11/12 Dec—continuing this southern trend for the foreseeable future.


Mid week annotated weather map (see text for decode)

NZ/Tasman Sea

Between the migratory Highs there is room for a few troughs.

One is expected to move off the east of the North Island on Monday. Another is expected to deepen into a low as it crosses southern NZ on Tuesday and Wednesday. Without reprieve another Low is expected to deepen as it crosses NZ on Thursday and Friday- deepening to 980hPa as a large Low south of Chatham Islands. This Low is expected to support strong to gale SW winds and heavy SW swells in the Tasman Sea on Wednesday/Thursday. Avoid.


See my yotpak at for terms used.

Weathergram with graphics is

Weathergram text only


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Pattern and Chaos

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  1. Hello Bob. I have tried to contact you through your old Met office email but it may not reach you. I am trying to find evidence of any changes to the climate in New Zealand as forecast by NIWA. This is for a presentation I am doing for local community groups in Northland.. If you can help with this I would be very grateful. Bib Bingham.

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