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

02 December 2018

Bob Blog 2 Dec



Compiled Sun 02 Dec 2018


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.


Review of November weather:

Sea Surface temperature anomalies as at end of November may be seen

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is now getting warm enough to almost be called an El Nino event.  There is currently a patch of warm water around NZ, but this may change during the next month or so, affecting the NZ summer.  There is also warmer than normal conditions between Solomon Islands and French Polynesia, and this may add oomph to the South pacific Convergence zone. 

The Gulf Stream off the east coast of North America and the Kuroshio current off Japan still stand out, which is unusual so late in the year.

To see how the annual weather cycle and the seasons are working out, check the average isobar maps from

The subtropical ridge in the southern hemisphere has weakened and gone north in November.

Zooming into the NZ area, there has been a radical drop in pressure north of 45S, the 1015hP isobar has retreated  well to west and east of the Tasman sea, and the tropics have dropped to below 1010.  Sure enough the weather features in the Tasman Sea were decided troughy (after a month marked by blocking highs).  I suppose December will either continue with a troughy Tasman or continue the rhythm and have some blocking highs. Wish we could tell in advance, but weather is a mix of pattern and chaos.


The last 30 days of rainfall, and its anomaly are seen at

The rain map shows extra convergence around  and to the north of the Solomon Islands, and also that the Intertropical convergence zone and the South Pacific Convergence zone seem to be shifting toward the equator--- an El Nino trait.



Latest cyclone activity and TCFP tropical Cyclone Formation Potential as seen at or

Tropical depression 05P /97P has deepened to 993hpa in the Coral sea and is expected to continue to deepen over next 24 hours and go south and then go west, but may fade before it gets to northern Queensland.   It is quiet elsewhere for a change.


SPCZ=South Pacific Convergence zone.

The SPCZ is active and moving south. it is likely to visit Fiji by mid-week, maybe the Loyalty Group to Minerva on Thursday, and maybe Tonga by local Friday.

Subtropical ridge (STR)

A new HIGH is expected to travel eastwards into the South Tasman sea by Wednesday and then go NE into central Tasman sea by the weekend.  It is a slow-moving system and may fade around Wed 12 Dec and the be replaced by another High reaching northern NZ around sat/sun 15/16 Dec.


Tropics to New Zealand

Trough is expected to bring a W/SW change to North island during Tuesday and then that High in the Tasman sea should maintain a southerly flow over northern NZ until end of next week.  Departures from the tropics before Thursday will encounter weak headwinds near NZ.

Between Tropics and Australia.

The High moving into Tasman Sea from mid-week means easterly winds from New Caledonia to Australia, good for sailing to Australia.  If wanting to go the other way, then depart before mid-week or go well south to avoid the easterly winds.


From Tahiti to Tonga

Trough related to the SPCZ is likely to reach Tonga by local Friday and then travel east.



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