Meteo

The regular availability of reliable weather forecasts is obviously essential during an ocean-passage: patches of bad weather or, conversely, of light winds that need to be avoided, more-or-less favourable wind direction and consequently the best routing strategies (seldom the straight line turns out to be the best choice!), etc.

Having an SSB radio, equipped with a Pactor modem which is an excellent meteo-fax demodulator, we had the possibility to receive both voice forecasts as well as the classical meteo-faxes.
Sadly, both options turned out to be of limited value, also due to the inaccuracy of published frequency- and time-tables.
Furthermore, understanding forecasts in a foreign language is not always easy, while receiving a series of weather charts implies keeping the SSB and the PC switched on for a long time, with a severe penalty on the batteries.

As it turned out, the only areas where we systematically listened to voice forecasts have been the Mediterranean and Australia, and we never used meteo-faxes.

Navtex would have been a good and low-power solution to receive text-forecasts, but unfortunately that’s not true everywhere due to the patchy implementation of Navtex stations around the world.

Practically all the Rally yachts gradually converged on a strategy similar to our, which was as follows:

- subscription, on the (free) “saildocs” service, to a 6-hourly e-mail message with the relevant Met-Area’s text forecast.

- subscription, again via “saildocs” to a 6-hourly email with a “grib” file covering our intended sailing area and giving present situation, 12 hour forecast, and 24-48-72-96 hour projections.

Every time we connected to Sailmail (at least once a day, more often twice) the system took care of sending us only the latest messages (deleting the older ones we had not downloaded), so we were sure of always having the latest info.

The usefulness of the text forecasts (typically the very same that are – sometimes – broadcast over Navtex) has been very variable, good in the Med and in the Atlantic, as well as around Australia, quite mediocre in other areas where the Countries in charge of the forecasts do not seem to bother too much.

On the contrary, we all found the reliability and usefulness of the “grib” files to be very good, especially in open sea. Fed into a dedicated software (there are many available for free) these compact data packages produce weather charts not much unlike the classic ones broadcast by the much slower fax system.

Example of GRIB-file display from a chartplotter application;
at the touch of a button the weather evolution over a period of several days can be analysed

The trick is to keep the data file size low, to keep transmission times over the SSB within reasonable values, and this is achieved by limiting the size of the geographical area, keeping the page interval not too short and keeping the data grid rather wide.
The Grib files are produced for all over the world by means of computerised models, and are therefore rated as potentially inaccurate especially near land, but our practical experience has been very favourable, and we all found offshore accuracy to be quite good.

When near land and having fast internet connections available, many preferred to access the same grib files with the “U-Grib” web-based service: nicer and user-friendly interface, but a fast connection is needed!

Webmaster: Gianfranco Balducci - email: gfbalduc@tin.it

Last Update: 07/09/2017

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