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

22 May 2016

Bob Blog 22 May 2016



Issued 22 May 2016


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.


William (Bill) Gray, the founder of seasonal Cyclone forecasting, discoverer of cycles in hurricane activity, and Professor Emeritus of Colorado State University, died last month at age 86. This blog is dedicated to his memory.


El Nino

As we move into the time of year that the El Nino parameters typically change El Nino , we can see the current El Nino episode by looking at the Southern Oscillation Index (SOI) which counts the number of isobars between Darwin and Tahiti, and thus comes from the atmosphere. This s gradually weakening, but in a stuttering fashion. We can not tell if its latest stutter is its last.

A good view can be gleaned from


An El Nino episode occurs when there is an excess of heat energy being stores on the planet. This heat is stored mainly on the eastern side of the planet’s largest Ocean, namely around the eastern equatorial Pacific. The NIN3.4 index measures this storage and is showing temperatures in the target area are definitely returning to normal levels. A comparison with last mega El Nino in 1997/1998 can be seen from latest graph at, and shows this mega El-Nino was slightly stronger and has lasted longer.


The Tropics

TC ROANU brought the worst floods in 25yeras to Sri Lanka and led to a death toll of at least 24 people in Bangladesh (2 million people relocated by its storm surge).

This brings a wet start to the Indian monsoon… but the rains are weeks away from NW Indian. NW Indian is having its annual pre-monsoon heat wave, but this year has already broken records with 51C measured in Phalodi, in the western state of Rajastan last Thursday.

Rain maps for the past fortnight from show cyclone ROANU in the Bay of Bengal.



SPCZ=South Pacific Convergence zone.

SPCZ is expected to remain draped from PNG across northern Vanuatu to the Tokelau/Samoa /Suwarrow/north-of-Tuamotu area, with a touch over northern Vanuatu from Tue to Friday local.


STR= Sub-tropical Ridge

The next HIGH over Australia is expected to move into the northern Tasman Sea on Wednesday and fade by Thursday. Next High departing Australia is likely to do so on Saturday, and may linger in Tasman Sea until mid-next week.


Voyage Outlooks:

Panama to Galapagos:

Light to moderate southerly winds around Panama this week, so not a good week to depart.


Travelling to Marquesas:

Winds near Isla Isabela are expected to be southerly this week and best for departure on local Mon to Wednesday. May as well get best from the current by going to 4S then west to 130W and then direct. Light winds are expected over Marquesas from local Monday to next weekend.


Tahiti to the west

The SPCZ has shifted to north of Tahiti and Tuamotu so this week should have more settled weather than last week for a departure. Since the SPCZ is likely over the northern route, take the middle route (Palmerston/Niue), or southern route (Aitutaki/Beveridge reef) rather than the northern route via Suwarrow.


Between NZ and the tropics

Another week of boisterous westerlies over northern NZ with one deep Low from Monday to Wednesday and another on Saturday and Sunday.

May be better to stay put until next week, unless you want to go east towards Tahiti.


Between Australia and New Caledonia

A Monday departure is looking best this week, but may have light winds for starters.

A Tuesday departure may encounter strong winds from a front near 160E on Friday.

A Wednesday departure may encounter strong winds from a front near 157E on Friday

A Thursday departure may encounter strong winds from a front at the start.

And a Friday or onwards depart may encounter lots of easterly winds east of 160E.


See my yotpak at for terms used.

See my website for information on tailor-made voyage forecasts–

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