BOB's BLOG

WEATHERGRAM
YOTREPS
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 Niqo is in the early stages of developing and may reach
moderate strength moving forward into mid- to late (northern) summer of
2014."

WEATHER ZONES
Panama to Galapagos: There is a burst of NE winds across Las Perlas at
present and this is expected to last until Tuesday 1 April local. Voyage map
in my graphic blog shows the forecast for a yacht that can motor/sail up to
6 knots may encounter taking off from Las 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.

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 boatbooks.co.nz/weather.html for terms used.
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