Weather Forecasts on Issuma

Issuma has several ways of receiving weather forecasts.

While in USA and parts of Canada, there are the VHF radio weather channels providing continuous voice forecasts.

Like most boats, Issuma also has a barometer for weather forecasting. This is just a regular barometer, from which the pressure is read and recorded in the logbook hourly.


There is a Furuno FAX-30 weatherfax receiver, which is programmed via web browser on a computer (connected via Ethernet), to receive forecasts at specific times from specific stations. Up to six weatherfaxes are stored in the weatherfax receiver before being overwritten by later faxes. The fax images are viewed via web browser on a computer (and can be printed from the computer). When I got to Canada, I found I needed to buy an antenna amplifier (Furuno FAX-5) before I could receive any Canadian weatherfax transmissions.

weatherfax as received

The weatherfax receiver is set to receive particular frequencies at particular times. The NOAA division of the US Government very helpfully compiles a list of all weatherfaxes and what frequencies and times they are broadcast at from stations worldwide and distributes this freely as a PDF file (Worldwide Marine Radiofacsimile Broadcast Schedules). Which stations can be received depends on how far away the boat is, and which frequencies (most stations operate multiple frequencies) are best depend on the time of day (at both transmitter and receiver).

How useful the weatherfax receiver is depends on what part of the world you are in. It takes a noticeable amount of power, and is probably most suited for boats with generators. If you are in an area covered by faxes from the USA, you tend to get good reception and a wide range of weatherfaxes to view (wind, wave, sea-level pressure and 500mb forecasts for 24, 48 and 96 hours). In the South Atlantic, the area near South Africa is covered by South African weatherfaxes. Chilean weatherfaxes give you an idea of what weather is coming to the southern South Atlantic (as the weather tends to come from the west), but I've never talked to anyone who has received weatherfax transmissions from either Argentina or Brazil (perhaps I needed the weatherfax antenna amplifier?).

This year I put a printer onboard, to help with interpreting the weatherfaxes. It is much easier to understand the progrression of weather systems when several faxes are laid out on the table at once, rather than having to flip back and forth between different screens on the laptop.

The weatherfax receiver is most useful at sea, far from land. In port, or near land, fewer or no faxes are received.

GRIB (Gridded Binary) forecasts are detailed forecasts for all areas of the world, made by computer models. They are not as accurate as forecasts put out by human forecasters, who look at several computer model forecasts and use their experience to judge what will be most likely for a particular area. While not as accurate as what a meteorologist can come up with, the GRIB forecasts are detailed down to small areas (ie 1 degree square latitude/longitude areas), and are available in 3 to 6 hour increments, going out as far as 7 days (though with much less accuracy after 5 days).

GRIB image in GRIB viewer

We receive GRIB forecasts (usually from the GFS model) via emails to/from, a wonderful resource for cruising sailboats. For information on how to receive GRIB files by email and what types are available, send a blank email to

Also via email, we usually receive the GMDSS forecasts for the Met Area we are in. There are several Met Areas in the world, and different countries generate the forecasts for different areas. Email is NOT the way the GMDSS forecasts are meant to be received (they are for things like INMARSAT C), so sometimes there are delays in receiving them that make them useless, but they are nice for getting an overall idea of the forecast that has been done by a meteorologist. Because these are for large areas, they are not very detailed, tending to indicate the maximum winds for an area over a 12-24 hour period of time. They are helpful to read in conjunction with the GRIB forecasts. .


NAVTEX receivers are great things to have in countries that have NAVTEX transmitters. You just leave the device on, and read the forecast (and any navigation warnings) on the screen when convenient. The Furuno FAX-30 can receive NAVTEX forecasts, though Issuma also has a dedicated NAVTEX (Furuno NX-300) receiver.

Some NAVTEX receivers (like NASA's) take very little power to operate, as all they do is sit there and receive. The Furuno NX-300 NAVTEX receiver insists on having the screen backlit whenever it is on, so uses much more power than necessary.

Somewhat similarly to weatherfaxes, NAVTEX reception is better at sea than in port.

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