A little more than 10 years ago I first cruised in the South Pacific among the Solomon Islands and Vanuatu. One of the characteristics of these locations was the lack of navigational aids, which placed heavy reliance on the best nav tool we had — our eyeballs. But another characteristic was the poor visibility of the water, making safe passage among the reefs best done in clear, sunny weather.
In those days we relied heavily on the movement of the Tropical Convergence Zone. When the TCZ was in our area, the weather was characteristically rainy and overcast, making movement among the reefs and islands a bit challenging, and in some cases downright dangerous. Though weatherfaxes don’t show TCZ data, we managed to find it.
The good news was that a daily Morse code broadcast from Wellington, New Zealand, (ZKLF) on weatherfax frequencies, gave us the ability to draw a weather map using the IAC Fleet Code format. The information originated from the weather office in Nadi, Fiji. The bad news is that ZKLF has discontinued sending the IAC Fleet Code.
The IAC Fleet Code format is stylized information in five-number code groups, which, when used with a decoding book, enabled us to draw weather maps by hand by connecting the dots to show the location of pressure, frontal and tropical systems. The latter contained the TCZ information we were seeking — the information that was lacking from the available weatherfaxes. After a few months of listening to the broadcasts, writing down the five-number code groups, decoding the location and plotting the lines between the dots, we became adept enough to plot the dots as we listened to the Morse code broadcast.
Now email and display programs together provide a nearly instant determination of that sought-after information — the convergence zones.
Obtaining Fleet Code bulletins
Instead of listening to a broadcast and copying the broadcast data by hand, today’s email-equipped voyaging boats have two options for receiving the information: SailMail/Winlink 2000 and Yotreps.
When using either SailMail or Winlink 2000, you can subscribe to a free service called Saildocs. This is an automated server that supplies weather bulletins and other documents via email. The Saildocs service was created by the author of Airmail, Jim Corenman, and is supported and operated by the SailMail Association (www.sailmail.com) for its membership. In addition to a wide variety of text weather bulletins, Saildocs also makes available grib weather-data files. Saildocs is an email-based system; for more information send a (blank) email to: firstname.lastname@example.org.
A fleet code bulletin is available from Saildocs titled “fleet.nadi.” This is the same information we copied laboriously via Morse code. The area of coverage of the Nadi broadcast is from the equator to 35° S and from 150° E to 120° W.
This information also is available from the Yotreps list server, operated by Mike Harris at Pangolin (www
.pangolin.co.nz). Send an email to email@example.com with the words “Fiji fleet” in the text body, and you’ll get a message posted back to you. You can join the list and receive regular copies of the postings until you unsubscribe. Help on the use of the Yotreps list server can be obtained from www.pangolin.co.nz/yotreps/
list_manager.php or by sending an email to firstname.lastname@example.org with just the word “help” in the text body.
Displaying the data
Displaying the information received from either source is effortless, compared with the hand plotting of years ago. A free program, PhysPlot (version 1.001 Beta release), is available for download from Pangolin and does this quite nicely.
The bulletins received from either Saildocs or Yotreps are contained within a message and must be cut and pasted into a file (I use Notepad) and saved in .iac, .txt, .zip or .exe format.
When the saved file is opened with the PhysPlot program, you get a display like the one on page 59. City locations are displayed by clicking on the yellow dots. I’ve drawn arrows to show the pressure and frontal information.
Although this pressure and frontal system activity is normally shown on weatherfaxes, the thing we’re after is shown by the orange lines, the tropical systems.
If you scroll down on the left, you will display the information on tropical systems. And there we find the lines and zones of convergence.
The changes in the convergence zone can be tracked easily by keeping daily records. (Taking snapshots of the screen and saving them in a file is a described in Image Logs, Issue 144, March/April 2005.)