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

28 June 2015

BobBlog issued 28 June 2015



Issued 28 June 2015


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.


The Brisbane to Noumea 2015 Yacht race started on Saturday 20 June and, as luck would have it, was undertaken in a near perfect weather pattern:  Almost a beam reach the whole way but wind gets forward of the beam near New Caledonia.  Winning yacht was Beau Geste taking 2 days 43 minutes and six seconds – a new race record.

See for all the info.


In The Atmosphere:

The Southern Oscillation Index SOI sums up the weather pattern over the South Pacific in one number and is based on the standardized difference in the barometer readings between Tahiti and Darwin (30 day running mean). The weekly update was lower than -10 for four weeks in May, enough to start a moderate El Nino episode. A couple of weeks ago the index went positive, and last week it was negative again. Possibly these fluctuations can be explained away as due to passing troughs over Tahiti.


SOI is shown at




No Tropical Cyclones at present but a very interesting thing is happening along the equator near Papua New Guinea . It is called “equatorial westerlies”. This burst of wind started off from the Asian monsoon and is best seen at the 5000ft level (lower cloud level) to clearly show how it is producing eddies, helping create tropical lows—three in the Northern Hemisphere just north of 5N and one in the Southern hemisphere just south of 5S. Equatorial westerlies may be  seen at on


The tropical depression in the southern Hemisphere already has the name TD17F and seems to have  a very good chance of being a named tropical cyclone over the next few days, Its central parts may track across western parts of Solomons on Tuesday, but the main damaging winds are in a ring about 50 to 100 miles from the centre and are likely to visit all of Solomons. BRACE FOR SQUALLY GALES, HEAVY RAIN (150-250mm/day) AND HIGH SEAS especially Tuesday and Wednesday.



The Indian Monsoon has been progressing stronger (in wind) than normal over past week, but the clouds stalled for a time so that there was a heat wave up to 44C over Karachi (peak temperature on 22 June), with over 1200 related human deaths.


Monsoon progress may be seen at


The weekly rain maps over the past two weeks show the monsoon rain moving onto Burma/Myanmar and intense rains already inTD17F to northeast of Solomons.

These weekly rain signatures may be seen at




SPCZ=South Pacific Convergence zone.

SPCZ section that is over Solomons is expected to drift into Coral Sea from Wednesday. The section over the Southern Cooks is expected to form a LOW that travels SE to south of the Austral Islands and deepens further as it turns south over the weekend.


STR= Sub-tropical Ridge

STR is expected to remain strong this week along about 30S. However there is a weak spot between NZ and Fiji. The computer models have been trying to produce a trough in this region. Note that there is a squash zone of strong enhanced trade winds from near west of Fiji to Coral Sea between SPCZ and STR.


Mid latitudes

Intense trough is expected to move across NZ from Tasman Sea on Thursday and Friday, preceded by strong NE winds, accompanied by wind change and rain, and followed by strong SW flow and bug swells on Saturday and maybe on Sunday 5 July. Then another trough is expected over northern NZ on Tue 7 to Thu 9 July.


Departing from Australia to the tropics this week:

After the great weather pattern for the Brisbane Noumea 2015, the way from Brisbane to Noumea has been blocked by too many headwinds, and so shall be the case until Wednesday. There may be an opportunity after the Thursday SW winds in the Tasman Sea ease.


Departing from Northern NZ going north.

It looks OK to depart Mon/Tue but I think these departure will need to negotiate NE winds by Thursday and a passing front on Friday. These negotiations may be at 30 to 25S where the front is expected to be tame, so these voyages may be OK--- but not the best. At this stage weather pattern for a departure on Sun 5 July is looking more comfortable.




See my yotpak at for terms used.


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