Bob McDavitt's ideas for sailing weather around the South pacific

27 April 2014

Bob's Blog issued 27 April 2014

Issued 27 April 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) was in the pink (below minus 10 in the graph for much of April but is now blue again.

No tropical cyclones around tonight, but the International Tropical
Convergence zone has been active across the entire Pacific and over Central
America. Also there was an almost-cyclone that brought a period of wind and
rain to Gulf of Carpentaria and threatened the Timor Sea.

The recent deadly avalanches on Everest are noteworthy. The glacial melt
lakes in that region have been growing since the 1980s. Most (but not
all) glaciers in the region are shrinking because of a drop off in regional
rains during the monsoon and winter months. Apa Sherpa used to have a farm
until it was claimed by a glacial lake outburst flood in 1985 and then he
became a climbing guide. According to Apa: In 1989 when I climbed Everest
there was a lot of snow and ice, but now most of it has just become bare


Panama to Galapagos: The wind flow over Panama and Las Perlas is expected to
be light and variable over the next few days. Also the wind flow for much of
the distance between Panama and Galapagos is expected to be from the SW this
week, as was the case last week, no good for this voyage. And so it may be
worthwhile waiting another week (or more) for this trip, sad to say.

Galapagos to Marquesas
If departing in the next few days with a vessel cruising at up to 6 knots
then head off to south of the direct path at the start along 244M/248T to
2deg 30min S then WSW along 250M/262T for around 1888nm then go direct to
Fatu Hiva.

SPCZ South Pacific Convergence Zone
This stretches from Solomons to Fiji. There is also a convergence zone from
Tonga/Samoa to French Polynesia, found on the north end of the squash zone
of enhanced trade winds and NE winds that mark the north end of a large
intense High with centre near 45S.
A tropical LOW may form south of Tonga by Wednesday 30 April and travel
south along 170W.

STR Sub-tropical Ridge
The STR remains in its normal winter position, stretching from the deserts
of inland Australia across the North Tasman Sea and generally along 35 to
45S to the east of NZ.

New Zealand area
A front is on its way to cross Northland on Monday and then a squally trough
is expected on Tuesday.
This is followed by a W/SW flow on Wednesdaythe best weather pattern for
departing to the north this week, and then a passing high with light winds
on Thursday.
A large trough/low is expected to deepen rapidly off Tasmania on Saturday
3 May and then cross the Tasman Sea /NZ area early next week. The NW flow
ahead of this system should start over Northland from Friday.

Departing from NZ to the tropics
30 April is the nominal end of the Southern Hemisphere Cyclone season so
many yachts may want to depart Northland then or in early May. It seems to
me that the best day to depart this week is with the W/SW winds on

See my yotpak at for terms used.
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