Weathergram 18 Nov 2012



Issued 18 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.

This week’s edition is shorter than usual while I attend a Met Society conference in Wellington.

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 since start of October, and was 0.35 on 18 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: There’s a tropical depression in the Bay of Bengal, heading SW to Madras. Otherwise all is quiet.


South Pacific Convergence Zone SPCZ

The South Pacific Convergence Zone SPCZ has stayed in place from Solomons to the Tuvalu/Rotuma/Tokelau area, and is slowly intensifying. There are now some west to NW winds near the equator to north of Solomons and this is a danger sign that a tropical depression MAY form on the SPCZ during the next week— most likely around Vanuatu or to east of there. Moving to south of Fiji by the end of the week. This bears watching and it may be a good idea to stay put if you are in the target area this week.


The STR is likely to be shifted south this week down to the NZ area makes a zone a light and fickle wind that is hard for sailing but good for motoring.


Mid week weather map (see text for decode, click to enlarge)

NZ/Tasman Sea

A low is expected to form over the Lord Howe Island area on Monday and then move east and merge into a trough over northern NZ.

With high pressures over central NZ and lower pressure to the north and south, it is likely to be a trough week for anyone approaching Northern NZ. The NE winds ahead of this trough may be OK for sailing south, but when they turn to be from SE , as on Friday-sat-Sun 23-24-25 Nov, they may be blowing against you.


See my yotpak at for terms used.

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Pattern and Chaos

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