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

08 October 2017

Bob Blog 8 Oct



Compiled Sun 08 October 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.


Its Palolo season this week: On the last quarter moon there is an overnight full tide, the first since the equinox, and that’s the trigger for a spawning of a coral worm called Palolo. They drop off their tails or pod; jade for female and brown for male and these mix together in the swirling tide, with each having a light-sensitive spot that directs them all to the moon a sit sinks in the west. At dawn the pods dissolve allowing eggs and sperm to get together and start a new generation. The rising is only on the turn of that one tide, taking place in a few hours.

If you get the chance ask locals in Vanuatu/Fiji/Samoa/Tonga for more.


FLEET CODE (my annual mention)

FLEET CODE was established to allow a weather map to be sent to the whole Fleet all at once via Morse code transmitted over Shortwave. Fiji Met Service are still manually converting their analysis map into fleet code and, thanks to Mike Harris of Pangolin and the people at saildocs these maps can be downloaded as email and drawn on your own computer as you travel around the South Pacific.

They have an advantage over GRIB files in that they contain convergence zones, as seen by Fiji Met Service meteorologists using satellite imagery to fine tune placements.

To download the latest Nadi Fleet code send an email to, no subject needed, saying SEND nadi-fleetcode.

When you receive the reply email, use something such as notepad to save the data as a text file and store this, say, on your desktop, as, e.g. fleet.txt

Mike Harris’ PANGOLIN website contains a page which allows you to save a beta version of PhysPlot. Go to . This is a windows program physplot.exe (now called a desktop ap) which can open that file fleet.txt and turn it into a weather map for you.

I don’t use OPENCPN, but apparently you can download the fleet code plug in from website and this gives better viewing of the overall area.



TC NATE developed over central America and deepened as it travelled north across Gulf of Mexico , and made landfall tonight over Alabama, and is weakening as it goes inland.


Looking at the weekly rain maps from last week and the week before, we can see that there is an increase in area of rain activity in the South Pacific, and in the area and intensity of rain across the equatorial part of the Indian Ocean.

See for weekly rain maps.



SPCZ=South Pacific Convergence zone.

The SPCZ has been lingering in place this week from Solomon Islands to Tuvalu/Tokelau area. Its eastern flank may shift south and visit Samoa later this week and extend southeast Southern Cooks next week.

There is likely to be a squash zone of enhance SE winds and south to southeast swells over 3 metres across the French Polynesian area from Wednesday to Saturday (UTC). May as well stay put for this.

Tropical accumulated rainfall for next week can be seen at from


Subtropical ridge (STR)

HIGH 1 is expected to travel east along 45 to 40S from east of NZ on Monday to south of French Polynesia by end of the week. It is this high which is forecast to be responsible for the squash zone over FP late this week.

HIGH2 is expected to spread into the central Tasman Sea on Wednesday and then travel northeast across northern NZ on Friday and to east of NZ along 35S from Saturday.


French Polynesia to the west:

Be mindful of that squash zone and increased swells near French Polynesia from Wednesday to Saturday (UTC). May as well stay put for that.


From tropics to NZ or Australia

The Island Cruising Association are supporting the All Points Rally, from all major parts of South Pacific to Opua ending in a ten days of activities 15 to 25 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. See to register.

Further west there is the GO WEST Rally. From New Caledonia to Australia, culminating with Welcome week events in Bundaberg, 6-12 November. It’s NOT too late to join the rally and enjoy a tailored voyage. See Registration includes standard Australian clearance fees, and these are around $A400.

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 SPCZ South Pacific Convergence Zone as it sometimes brings squalls, but is well to the north this week.

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 a passing trough on Monday, and no strong winds this week. .

2.The second factor to watch is the STR, or subtropical ridge, where the HIGHS travel, 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 squash zone expected near French Polynesia later this week.

3.The third factor is weather for arrival. Try to avoid bursts of strong southerly winds and heavy swells during the trip or upon arrival. These come from the Southern Ocean and occur 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 does its own thing.


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

Between Tropic and NZ

1 and 2 are OK but 3 has problems. Avoid the SW winds near NZ on Tuesday and Wednesday. Winds are Ok for arrival on Thursday to Sunday, then NOT OK on Mon/16 to Sat 21 Oct next week.

If it takes you around 8 days to get to NZ then consider delaying departure to sometime later next week, or contending with some southerly winds.


Between New Caledonia and Australia

1and 2 are OK this week. 2 and 3 may have problems this or next week depending on your desired port of entry.

A Trough is expected to reach Sydney and fade near Coffs on Tuesday. A stronger trough should reach Sydney on Wednesday and fade near Coffs /Brisbane by Friday.

The HIGH that is expected to be crossing south Tasman sea on 15 to 20 Oct may cause a squash zone of strong easterly winds near 25S near Australian Coast. Avoid arriving there then.



If you would like more detail for your voyage, then check to see what I offer.

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