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

19 November 2017

Bob Blog issued 19 nov 2017



Compiled Sun 19 November 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.


For those of you who may be interested:  I’ve been invited to speak for an hour or so at 3pm Friday 24 Nov at the All Point Rally 2017 seminar being held by ICA in Opua.  I wonder what I should talk about-----


Some interesting photos of this month’s weather:

On Tuesday 7 November Bundaberg was hit by a passing heat trough with thunderstorms This visit was unusually windy, with wind gusts reaching 68 knots (image at courtesy of John Hembrow from the Downunder rally).


And I received an image from a yacht I’m forecasting for on its way across the equator towards Hawaii (Courtesy of Jono Wishart), taken at 11S 170W of a Brooks and Gatehouse monitor showing sea temperature of 35.3C where weather global model was forecasting sea temperature of 30C.   He says he has seem 35.8 since.



I’ve compiled a 3min 25sec video using to show the development of that Low on Friday 17 November --- the one I referred to last week as “Something to avoid” and if you have access to good Internet you can view this at website



It has been busy around Vietnam recently, and Tropical Sytem KIROGI  is currently heading west across the South China Sea onto South East Asia, but should soon fade.


Looking at the weekly rain maps from last week, and the week before, we can see some interesting bursts of rain in the Northern Hemisphere particularly in Bengal Sea, in North Pacific west of Hawaii, and from Cuba to central North Atlantic. There is also an increase in rain in the South Pacific Convergence Zone, especially from Coral Sea to Fiji/Tonga.



SPCZ=South Pacific Convergence zone.

The SPCZ is hovering from Coral Sea to northern Vanuatu to northern Fiji at present, and is expected this week to drift south onto all of Vanuatu and Fiji and maybe onto parts of Tonga. These areas can expect some random squally downpours.   Another convergence zone, a continuation of the main zone, is expected to be draped from Tuvalu to south of Samoa to parts of Tahiti. 


Subtropical ridge (STR)

HIGH H1 in the south Tasman sea on Monday is expected to move towards central NZ by Wednesday and off to the east of NZ on Friday.   It may be a useful HIGH for anyway intending to cross the Tasman Sea

 Weak trough should cross southern NZ on Thursday/Friday and deepen into a Low and it travels off to the south on Sunday. Then another HIGH H2 is expected to travel northeast from the southern Tasman Sea onto central NZ by Tuesday 28 Nov.   These are good conditions from anyone planning to ail west-wards across Northern Tasman Sea.


Between Tropics and NZ

The Low to NE of NZ is already moving away, and today’s data shows it is followed by a week or more with High pressures dominating over NZ and thus easterly wind from tropics to NZ, so if anyone is still waiting to come south then this week is looking OK.

Winds may be variable near northern NZ from Fri 24 to Mon 27 Nov due to a passing trough.

Note that there may be a squash zone of strong SE winds on the northern side of the High over NZ from Tuesday to Thursday, near 20S.


The Sea is the last free place on earth

- Humphrey Bogart


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