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

13 November 2016

Bob Blog 13 Nov 2016

Compiled 13 November 2016
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.

Thanks to the generosity of 24 donors. the "weather stations for Tonga"
fundraiser at raised $615 in the past week, 2% of it's goal.

Many of us know there are gaps in the Google earth data. Here's a link to a
recent blog written by Max Shaw of Fluenta, introducing another app SAS Planet
(an alternative to Ovitel Maps).

Also Max and I have noticed that has recently added ECMWF data
to their sites. I recommend ECMWF data, especially in the tropics. At present
GFS and GEM have the idea of a Low in the Coral sea by Fri 18 Nov, but ECMWF is
showing nothing there until Tue 22 Nov. ECMWF is more reliable. To learn more
about's use of ECMWF data

And you may know that Tuesday's full moon is the closest and therefore the
largest since 1948. Tides are not exceptional. They depend on harmonics of sun
and moon gravitational forces, so having a closer moon is not a guarantee of
extreme tides-mind you if you have been taking shortcuts across a sandbar or
reef recently then take care at low tides over the next week.

The Tropics
After a few busy weeks, the tropics seem to be taking a rest for now.

There has been flooding, ponding and slipping around parts of New Zealand.
---and just now a severe long-lasting lateral quake
revised to M6.6 then M7.5, plus a tsunami warning for South Island East coast
To see the Tsunami arriving in Kaikoura and Wellington and Christchurch:

Rain accumulation maps looks less intensive rain in most areas, but an increase
around Samoa.
Rain for the past fortnight from


SPCZ=South Pacific Convergence zone.
SPCZ: The intensity that built up over Samoa during the past week is likely to
move towards French Polynesia this week, but in a disorganized fashion. May be
some small tropical lows forming on the zone this week with squally showers. but
models don't have anything deepening at this stage. We do have a MJO event
occurring at present but no organised equatorial westerly winds, so maybe just a
few tropical lows are likely.

Tropical accumulated rainfall for next week may be seen at from

Subtropical ridge (STR)
Small high travelling east along 30S between Fiji and NZ tonight and moving off
to the east.
Next High in Tasman Sea is not expected until Thursday and is then expected to
travel slowly east along 30S. This is likely to be followed by a weak trough and
then another even slower and larger high next week, so this should offer a good
weather opportunity for yachts wanting to travel from tropics to NZ or

Tasman Sea/NZ Area.
There is a parameter called SAM (Southern Annular mode) that measure the
strength of the Polar Vortex (the ring of winds around Antarctica), and when it
goes negative there is an increased chance anywhere in the Southern Ocean for
polar chilled SW winds to burst further north. It's now negative, but forecast
to turn most positive week.

There was a polar blast off South Africa over last few days.
And now it looks like there MAYBE a small polar blast in the Tasman Sea and off
to northern NZ on Thursday 17/ Friday 18 Nov, with strong to gale cold and
squally SW winds with huge swells.
Swells over 4 metres may extend as far north as around 26S on Friday. These are
long period swells, sometimes called gentle giants, but somewhat disconcerting
sailing, so avoid.
After Friday, there should be good sailing conditions to NZ.
As of sailing Noumea to Australia: Looks OK after the trough clears off Noumea
on Wednesday.

Follow me on Facebook at
See my yotpak at for terms used.
See my website for information on tailor-made voyage forecasts-
Feedback to
Tell anyone you like that to subscribe they should email me.
Weathergram text only (and translator) is at
Weathergram with graphics is at,
Click FOLLOW at bottom right to subscribe.
To unsubscribe from WordPress: click the "unsubscribe" link on the bottom of the
email. Or, if email wasn't from WordPress then send a reply email saying LEAVE.

No comments:

Blog Archive