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

15 October 2017

Bob Blog 15 oct 2017



Compiled Sun 15 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.



The South Pacific/Australian tropical cyclone season is nominally from 1 Nov to 30 April.   A weak to briefly moderate LA NINA is expected to affect the tropical Pacific Ocean over the next six months. This tends to nudge the South pacific convergence zone to the south and west of its normal position, increasing the cyclone risk around Australia and Coral Sea, and perhaps reducing this risk in places east of the dateline.

The Bureau of Meteorology have considered this and say that the cyclone risk over Northern Australia is increased. The average number of cyclones per season across the entire region is 11.  Chances of more this season are 56%.


From note this image remains copyright to BoM, repeated here for educational purposes only.

Looking at the behaviour of the sea surface temperature over the past year, NIWA has searched the database for analogue years that may point the way as to how this season may develop. The top analogues are 1970/71, 1978/9, 1995/96, 2005/6, and 2007/8, and using this data they have compiled some cyclone risk maps.

In summary, NIWA and MetService is anticipating 8 to 10 named storms this coming season (compared to an average of 10.4), a normal to above normal risk for New Zealand, New Caledonia, and Papua New Guinea (mainly late in the season),  and a below normal risk for the southern Cook Islands, the Marquesas, and French Polynesia.

For more details see


Addendum to last week’s comment on Fleet code:

Chuck and Linda on JACARANDA say that :Once we open the email from saildocs we <Right> click the data.  A window opens up with some choices and we choose <export> The next window asks us where we want to export the data.  We have a folder already created called "Fleet Code".  We then just click <save> We also use OpenCPN as we like to see the data on an easier identified chart of the SP.  But we have also used Physplot in the past with good results.



During the past week a suprising development occurred in the mid North Atlantic ocean:  TC OPHELIA, the strongest such system this far east in the North Atlantic. Warmer seas are the most likely explanation for this. And its heading for Ireland on local Monday.  Reminds us of  “The Great Storm” 30 years ago in October 1987, but  this one is likely to bring warm dry gusty winds to southern UK.

 And over in the China Sea we have TC KHANUN heading for South China.


Looking at the weekly rain maps from last week and the week before, we can see a shift of heaviest rain from equatorial Indian Ocean to The Vietnam/Philippines region, and an easing of the rain over central America. There is also a stretching-southeastwards of the rain in the South Pacific.




SPCZ=South Pacific Convergence zone.

The SPCZ has been lingering in place this week from Solomon Islands to Tuvalu/Tokelau area and is expected to spread onto Fiji/Samoa and norther Tonga later this week.

An upper trough that is over the Niue area for the next few days is expected to descend and form a surface Low near 35S 165W by Thursday UTC.  This low is then expected to deepen as it travels south into the Southern Ocean, leaving a trough over the Niue/Southern Cooks area by the end of the week.


Subtropical ridge (STR)

HIGH  is in the central Tasman Sea tonight is expected to build to over 1032hpa by Wednesday and then slowly weaken and travel east along 30S this weekend to east of the dateline next week.   There is expected to be a squash zone of enhanced trade winds and rough seas on the north side of this High, mainly between 20 and 25S from 175E to the Queensland coastline on Wednesday/Thursday.


French Polynesia to the west:

Be mindful of the trough that is in the Niue to Southern Cooks area this week.


From tropics to NZ or Australia

The Island Cruising Association are supporting the All Points Rally, from all major parts of South Pacific to Opua ending in ten days of activities 15 to 25 November in Opua. Boats joining the rally are assisted with weather info, resources and planning tools to help make the passage to NZ as easy as possible. See  to register.

Further west there is the GO WEST Rally.  From New Caledonia to Australia, culminating with Welcome week events in Bundaberg, 6-12 November.  It’s NOT too late to join the rally and enjoy a tailored voyage. See Registration includes standard Australian clearance fees, and these can be around $A400.


Between Tropics and NZ

The High crossing the Tasman Sea is expected to bring lots of southerly winds south of 30S until Wednesday and then the squash zone associated with High may bring some strong SE winds near 25 to 30S on Thursday.   The High is expected to be followed by a FRONT reaching northern NZ on Sun 22 Oct, so avoid landing then.  That should be followed by OK conditions for arriving in northern NZ from Mon 23 to Thursday 26 Oct, and then a FRONT to avoid on Friday 27 Oct.   Note that Mon 23 Oct is a public holiday.


Between New Caledonia and Australia

There is expected to be a convergence zone along the Queensland coast on Monday and Tuesday. Avoid.

The squash zone associated with the Tasman High is expected o bring strong SE winds and rough seas between 20and 25S from 175E to the Australian coast on Wed and Thursday (crudely speaking), so wait until after this squash zone.

After the squash zone there is expected to be a ridge with light winds across the route from Sun22 to Wed 25 Oct, and then a prefrontal NW flow.


NZ Coastal Classic

This RACE departs Auckland on Friday for Bay of Island. Expect SW winds, fading at times, especially around Cape Brett.


If you would like more detail for your voyage, then check to see what I offer.

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