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

10 November 2019

Bob blog 10 Nov



Compiled Sun 10 Nov 2019

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 state of the ENSO

The Southern Oscillation Index SOI sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin.

SOI (30 day running mean) touched El Nino territory in mid-September but is now relaxing.

It was below -10 units on this Australian scale for  4 weeks. 


 SOI trend (x10) since 2016 showing us in neutral territory as at

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the widest and warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. When SST in the target zone (equatorial Pacific between dateline and Galapagos) are notably cooler/warmer than normal, this is called a La Nina/El Nino episode.


 Sea surface temperature anomaly as seen at

Nino 3.4 index has been in neutral territory since May, and spent 4 weeks cooler-than-normal in September.

SO both SOI and NINO3.4 parameters are in neutral territory for now. For  an outlook on  the possible  future,  go  to

which shows an erratic future with 1 model going for an El Nino and another for almost a La Nin, but most models staying in neutral territory.



The latest cyclone activity report is at and TCFP tropical Cyclone Formation Potential at

Pray tonight for those being hammered by cyclones such MATMO over Bangladesh, and NAKRI over Vietnam.  At least HALONG is staying over a mostly open ocean.

Large potential for development  this  week over the  Guam  area.



SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from PNG to Samoa and then to Southern Cooks.

Passing convergence zone trough over Australs and Gambiers this week.

Passing trough over Fiji tonight, Tonga on Tuesday,  and fading by Thursday.


Subtropical ridge (STR)

HIGH is expected to linger east of NZ near 40S 160-150W until midweek then move off to the east.  Has enhanced trade winds on its north side, but not intense enough for a squash zone.

Next HIGH should form near 30S  in North Tasman on Monday and  travelling east, passing north of  NZ on Wednesday  then  fading from  Thursday,  but lingering as  a ridge over  northern  NZ for  the  weekend.


Tasman Sea /NZ/Aus

Trough crossing northern NZ tonight and Monday. Ridge on Wednesday, then another trough on Thursday. A lingering ridge for the weekend., then a NW flow for most of next week.

Good to depart tropics this week for NZ – but after the passing trough (reaching Tonga on Tuesday).

For Noumea to Aus, OK this week if you time your trip around the travelling  High.

Avoid arriving in  Australia  on Sat/Sun 16/17 Nov due  a passing trough/low


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