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

16 October 2016

Bob blog 16 Oct

Compiled 16 October2016
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.

Regarding the notes I wrote last week about FLEET code, Chuck on JACARANDA has
replied as follows:
We use two methods to view it
Physplot - The easiest way to use this is to just drag the unopened email right
onto the fleetcode icon on our desktop. It automatically opens and loads.
(This is using sailmail)
By sliding the viewing screen slightly to the right the actual text appears and
you can read about what you are seeing on the screen.

We prefer this as it gives us greater visibility of the overall area. You can
download the fleet code plug in from website.
When referring to the Fiji Day LOW last Monday I noticed that the upper trough
responsible was also shifting a "Vorticity max" out of the Tasman Sea and onto
Vanuatu. See my Facebook post at
An upper trough penetrates the South Pacific convergence zone over Fiji on 10
Oct, causing winds to spin and spiral downwards forming a surface low over
Fiji=The Fiji Day low. The extra upward motion brought heaps of RAIN. and as a
sideline, an entity of the west side of the upper trough known as a Vorticity
Max is taken by the southwest winds aloft from the Tasman Sea onto New Caledonia
then onto Vanuatu.
Well, A village just north of Port Vila (Tongamea) had a significant HAIL STORM
as a consequence.
I received photos of this hail from my good friend Alex from Honiara Weather
We are having a full moon this weekend, and so next weekend is the start of the
last quarter of the waning moon. That's when the full tide is overnight, and
it's the first of these events after the equinox that triggers the season for
PALOLO. when the coral worms spawn. They drop off their worm-tails or pods; jade
(female) or brown (male); and these mix together in the swirling tide, with each
having a light sensitive spot that directs it towards the moon as it sinks in
the west (or to a flashlight). At dawn the pods dissolve, allowing eggs and
sperm to get together and start the new generation. The rising is only on the
turn of that one tide and only takes place for a few hours. Samoan Met Office
say Oct 22/23 is this year's best chance.
Ask the locals about this and if you time it right you may be about to collect
some of this rare delicacy, or photo it. They might look yucky, but taste really
nice on toast, something like caviar, so I'm told.
Bureau of Met and NIWA have both issued their cyclone forecast for the coming
season in the past few days-I'll cover that next week for you.
In the NW Pacific tonight we have TC SARIKA and HAIMA, see them at
And in the Atlantic, after a very destructive path last week from MATTHEW, we
have NICOLE keeping well offshore, but making a direct hit over Bermuda as a Cat
3 (Saffir-Simpson scale). The radar image of this can be seen at

Rain for the past fortnight (from show an increase
in convection over Philippines, the track of MATTHEW and NICOLE in the Atlantic,
and a burst of rain over Fiji thanks to the Fiji Day low, but a removal of
convection from Solomons as a consequence.

Tropical accumulated rainfall for next week can be seen at

Tropics to NZ/ Australia: - Strategy
This is the time of year that yachts are staging themselves in Tonga (or Fiji
or New Caledonia) and waiting for the right weather pattern for sailing to NZ or

The Island Cruising Association are supporting the All Points Rally, from all
major parts of South Pacific to Opua ending in a one-week seminar 16 to 20
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.
On arrival participants are welcomed to Opua and entertained with a week of fun
and games, entertainment and seminars on a range of topics. This rally is FREE
thanks to the assistance of Main Sponsors Bay of Islands Marina and Boatyard and
the Opua business community. See

Further west there is the GO WEST Rally. Again from any port (most are leaving
from Noumea) this time to BUNDABERG, with welcome week starting 6 November 2016.

In deciding upon a departure date, it's as simple as 1.2.3:

1.The first factor to consider is the local weather: the South Pacific
Convergence Zone SPCZ sometimes brings squalls, but is well to the north this
week and still recovering after being vented by the Fiji day Low last Monday.
However, we have a passing (mainly upper) trough over Fiji on Monday/Tuesday,
and this trough is expected to slowly cross Tonga area on Tuesday/Wednesday.
This trough is likely to bring squalls and maybe some strong SE winds, so better
to wait for it to go before departing.
Some like to use Minerva reef as an extra staging post since it is 1.5 to 2 days
sail south of Tonga, and just out of the tropics (so marine insurance that may
be void in the tropics may work in Minerva). But it only shelters you from the
waves (so long as they don't topple over the reef) and not from the wind or
rain. It has that passing trough on Tuesday (local) with some rain until
Thursday, and is only likely to have fresh easterly winds form this feature.

2.The second factor to watch are the HIGHS that travel along the Subtopic ridge
STR, that zone between the trade winds of the tropics and the disturbed
westerlies of the roaring 40s. This zone is usually near 30S, and if there is a
big high then on its northern side there is usually an accompanying are of
enhanced trade winds, what I call a SQUASH ZONE. This week there is a HIGH
moving along 30S from N Tasman Sea tonight to east of NZ on Wednesday, and there
is a squash zone between that High and the trough over Tonga, mainly on
Wednesday/Thursday. The next High should start further south and cross the
Tasman Sea from Thursday to north of NZ on Sat 22 Oct, without any squash zone.

3.The third factor is to avoid bursts of strong southerly winds and heavy swells
during the trip or upon arrival. These come from the Southern Ocean and on a
different pattern to the passing troughs in the tropics. Sometimes a southerly
burst inter-reacts with a tropical trough and things get nasty. Not this week.
You can use to see expected weather features at your arrival point
for the next week, and aim to arrive "in-between active features", but remember
that these outlooks are just ideas, and real world will do its own thing. Over
northern NZ there is expected to be a weak passing trough on Thursday, and then
northern weakening trough on Sunday 23, and then maybe some strong SW winds from
a passing southern Low on Mon 24/Tues 25 Oct. And over the Australian coast
there is a passing trough this Monday and another mainly south of 30S, on
Friday, weaker further north on sat/Sun. I think you can handle these fronts
with suitable waypoints/timing.

Let's apply this 1,2,3 rule to some popular destinations:

Travel between the Tropics and NZ:
If heading from Fiji or Tonga, wait for that trough to go first. Maybe Wed from
Fiji and Thu from Tonga. but that may change. Arrange waypoints so as to
encounter that Sun 23 over NZ front near 30S. That depends on boat speed, and
configuration, so will vary from vessel to vessel.

Travel between New Caledonia and Brisbane/Bundaberg area:
Trough that was over New Caledonia yesterday has gone east now, but there is a
squash zone between it and the Tasman Sea High. That should ease during Monday.
Then OK to go anytime, but expect to encounter a weak passing trough around next
Sat/Sun as you approach coast. If you arrive over the weekend then there's a
surcharge to pay.

Travel from tropics to New South Wales
No real point in taking the rhumb line for such a voyage as the subtropical
ridge should be gone around rather than thru. Instead head for Brisbane, and
around 158E turn to your destination. This should also give you the benefit of
the assistance of the East Aussie current. However, remember that there is an
active trof south of 30S on Friday 21/Sat 22 Oct.
See my yotpak at for terms used.
See my website for information on tailor-made voyage forecasts-
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