Bob’s Blog



Issued 30 March 2014

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.

SOI The Southern Oscillation Index SOI sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.

SOI (30 day running mean) has dived negative in the past few weeks. After a high late January/early February its 30 March reading was MINUS 1.18 units. IF an El Nino cycle is approaching THEN this usually shows itself around or soon after the equinox, so maybe this swing marks the beginning of a trend.

According to AccuWeather Long Range Forecaster Mark Paquette, “We are confident that an El Niño is in the early stages of developing and may reach moderate strength moving forward into mid- to late (northern) summer of 2014.”


SOI trend (x10) since 2011 showing the recent jump as at




Weekly rain signatures for past two weeks, showing the extreme rain path from TC MIKE and the wet trough that arrive over Aussie eastern seaboard late last week. As seen at


Forecast rain for the coming week, as seen at



Weather Zones (see text) as expected mid-week at 0000UTC on Wednesday (GFS model) showing isobars, Lows and Highs, wind, waves, rain, current, ITCZ, SPCZ and STR . Purple lines are upper flow.

Panama to Galapagos: There is a burst of NE winds across Los Perlas at present and this is expected to last until Tuesday 1 April local. Voyage map below shows the forecast for a yacht that can motor/sail up to 6 knots may encounter taking off from Los Perlas on the high tide on local Monday afternoon. This window of good NE winds closes soon after that.


SPCZ= South Pacific Convergence Zone

This is weak at present and should slowly rebuild mainly between Solomons and Fiji/Tonga. A small tropical Low with strong winds around it is expected to form between Niue and Southern Cooks on Monday UTC and then travel SE. Associated squally weather is expected to move over southern Cooks during the next 24 hour.


Thunderstorms and squalls tonight over Southern Cooks as seen on Google Earth

There is an interesting convergence zone that is expected to fire up along 5S between 90W (just SW of Galapagos) and all the way west to Marquesas. This zone seems to be related to the equinox and should weaken during the next few weeks.

STR= Sub-tropical Ridge

The STR is expected to maintain good strength between 45 and 35S with ridge-tongues sticking out well from transient HIGH centres. There may be a zone of enhanced SE winds on the north side of each of these HIGHS. One of these should be located between the HIGH that spends much of the coming week east of NZ  and that low forming between Niue and Southern Cooks.

The next transient high from the west is expected to travel eastwards along 45S to south of Tasmania on Sat/Sun 5/6 April.

New Zealand area

Sad to say, another dry week for the drought areas in parts of North Island, and NW of South Island.


Trough currently in the mid Tasman Sea is having difficulties penetrating the high pressures left behind by a ridge over central NZ by the large Transient HIGH east of NZ. These wet clouds need rail-tracks of
falling pressure to make traction— They are most like to go south and weaken, sideswiping the south end of the country.

The ridge has locked a layer of moisture near the surface that keeps appearing as low cloud by day or fog by night = anticyclonic gloom.

Another trough/low combo is expected to cross Tasmania on Wednesday and the South Island on Friday/Saturday/Sunday/Monday 4/5/6/7 April.

See my yotpak at for terms used.

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