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

01 October 2017

Bob Blog 1 Oct 2017



Compiled Sun 01 October 2017

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.


Last month

Sea Surface temperature anomalies may be seen at

There continues to be more yellow than blue, more area covered by warm anomalies than by cool anomalies, but the blue is getting darker where it matters - along the eastern Equatorial Pacific (a possible LA NINA signal). And there is still a warm river appearing along east coast of South America.

To see how the annual weather cycle and the seasons are working out, take a quick look at the average isobar maps from

In September, the subtropical ridge in the southern hemisphere shifted slightly north of its August position, with the disturbed westerly flow as far north as Bass strait to north of North Cape, somewhat further north than normal.  A large anomalous LOW remains over South Australia/South Tasman Sea and explains the seasonal variations in the region: the hot NW winds for NE Australia, and the wet westerlies for North island and wet NE winds for eastern South Island.  

There is a purple anomaly from Caribbean to Eastern USA -  That’s IRMA MARIA and their associates. 

The anomaly map shows that the ITCZ is further north than normal---this is a LA NINA trait.

The Atlantic hurricanes also show in the monthly rain map at



Remains of TC MARIA have travelled more than half way across the North Atlantic, and may affect UK in a few days. Otherwise, things seem to be quietening down for now. Then again, a new tropical system is expected to form off the Mexican west coast later this week.

Rainfall for the past week compared with last week, shows the paths of IRMA and MARIA with a peak over Puerto Rica.  Also a build-up of rain near 5S in the Indian Ocean.  See




SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay in place this week from Solomon Islands to Tuvalu/Tokelau area.   Its eastern flank may shift south towards Samoa by this weekend.

The Trough that is travelling to east of NZ tonight is expected to continue east and fade well to the south of the tropics on Tue/Wed UTC.  It is followed by a day or so of 3 metres + southerly swells from the Southern Ocean reaching as far north as 20S for Tuesday.  These swells are gentle giants with a period of 12 seconds, so very well spaced apart.

 Another trough is expected to travel east across Southern Cooks and French Polynesia late this week, and this may form a LOW further south.


Subtropical ridge (STR)

HIGH 1 is expected to move across Tasman Sea along 30S on Monday and Tuesday and then fade over northern NZ on Thursday and Friday. HIGH 2 is expected to spread into the South Tasman Sea on Thursday and then travel east across South Island and rebuild east of New Zealand on Friday and Saturday.

French Polynesia to the west:

There may be some strong SE winds near Bora Bora on local Sunday and Monday.

The next obstacle to consider appears from around the end of the week  -- and is a travelling trough over Southern Cooks / French Polynesia. 

If tossing up between going to Samoa or Tonga, then pick Tonga and avoid the SPCZ.


Between NZ and the tropics:

Avoid the strong W/SW winds and rough seas near NZ on Monday, these should ease away on Tuesday.

Then there should be a window of opportunity for getting to northern NZ from Tue 3 to Sat 7 October thanks to passing Highs. 

 There is expected to be a trough near northern NZ around Sun/Mon 8/9 Oct with strong NE winds and some rain. 

 Then there should be another period of acceptable weather to get to northern NZ until the next trough arrives around sat 14 Oct.


Between New Caledonia and Australia

It’s Ok to go to Bundaberg or Brisbane, BUT avoid arriving there on Thursday 5 October, for that is when there may be a venting of the heat trough. This trough is expected to travel east across the eastern seaboard of Australia on Thursday, and deepen into a Tasman Low offshore on Friday.  This Low should then travel east to northern NZ by 9/10 October.

The trough may bring squalls and lightning to Bundaberg and Brisbane ion Thursday, followed by a brief period of SW winds, so avoid. 

 Apart from that,  the Tasman low is NOT expected to have much impact on the New Caledonia to Bundaberg or Brisbane route.


Vanuatu Volcano

And, for the goodness of your health, stay away from Ambae Island and its active volcano, Manaro Voul.

This island, east of Espiritu Santo, inspired James Michener’s mythical Bali Hai.



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