Weathergram 11/11/12



Issued 11 Nov 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) is relaxing after a bounce back from its low of MINUS 1.01 back on 25 Aug. It has been hovering around plus 0.2 to 0.3 during October, and was 0.15 on 11 November. Not much change. It’s now in neutral mode. And forecast to stay that way for the rest of this cyclone season.


Tropical cyclones in the Northern Hemisphere are now quiet at last.

Bureau of Meteorology Australia have this to say about our cyclone season


Odds favour a near average tropical cyclone season for the South Pacific

  • Near average tropical cyclone activity is the most likely scenario for the full South Pacific region.
  • There is a tendency for average to below average cyclone activity in the western region of the South Pacific.
  • Climate indicators which affect tropical cyclone activity show that:
    • the tropical Pacific Ocean is currently neutral (neither El Niño nor La Niña);
    • near-El Niño conditions have been present in 2012 and have been considered in this outlook.


The current, neutral state of the El Niño–Southern Oscillation (ENSO) would historically suggest the South Pacific region as a whole would experience near average tropical cyclone activity during the coming season. However, warmer than average sea surface temperatures in the central equatorial Pacific in July, August and September suggests slightly reduced odds of above average (slightly increased odds of below average) tropical cyclone activity in the western region of the South Pacific this season. Historically, the model has shown high skill in the west. This outlook is for the southern hemisphere tropical cyclone season which is usually considered to be between 1 November and 30 April.


South Pacific Convergence Zone SPCZ

The South Pacific Convergence Zone SPCZ has slowly intensified during the past week and is mainly stretching from Solomons to Tuvalu to Tokelau to Southern Cooks. The tropical low that visited Tonga/Minerva last Wednesday (as mentioned in pervious weathergram) has taken a fair amount of moisture with it off to the southern Ocean. Part of the SPCZ is expected to move south onto Fiji on Tuesday and onto Tonga on Thursday or Friday this week.


The STR should remain robust between 25 and 30S across the South Pacific this week. This makes a zone a light and fickle wind that is hard for sailing but good for motoring.

By the way, there’s a solar eclipse around 13 2210UTC – See my previous Weathergram for more details.


Mid week weather map(see text for decode)

NZ/Tasman Sea

Trough is crossing NZ on Monday/Tuesday 12/13th and moving away on Wednesday 14th. Another is visiting on Thursday 15th, and another on Sat/Sun 17th/18th with disturbed westerly flows in-between. This week these troughs are expected to have little impact to north of 30 South.


This week is the opposite of last week. We have occasionally unsettled weather at the NZ end of the voyage and mostly OK weather in the tropics and the STR. Try and time your voyage to arrive in Northland between fronts.



I am supporting Jeanne Socrates (69) in her quest to complete a solo unassisted circumnavigation sailing (RTW) on her yacht NEREIDA. At this end I am watching her weather as she sails around the world.

Jeanne took off from Vancouver, Canada last month and is now entering into the trades winds west of California.

You can read about her adventures from her web site at and this links to her fundraising page at

If one of your loved ones has been taken by cancer and you like watching RTW sailing then I recommend you contribute to this site as a memorial.



See my yotpak at for terms used.

Weathergram with graphics is

Weathergram text only


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Published by metbob

Pattern and Chaos

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