There’s a newer article on this subject, see Weather Faxes… Offshore
We’re all familiar with listening to spoken weather forecasts on the VHF radio. But VHF has a line-of-sight reception and even an antenna on top of your mast can’t pick up a station more than 10 or 20 miles away. So what do you do offshore? First you probably need to get weather data packets downloaded to your computer and second you need to choose the hardware system for receiving that data. Satellite phones are increasingly affordable. Or you can use your HF Radio, (either Ham or SSB) to receive weather as data packets. Getting a weather report when VHF is out of range is a simple matter when you have an HF radio (either Ham or SSB).
More and more people are choosing Satellite phones as they become more affordable in purchase price and monthly fees. And now that you can add a SatSleeve to your iPhone (and some Androids) to turn it into a satellite phone I suspect this market will begin to take off. However the devices are still expensive and the monthly plans and additional data charges can be formidable.
We’re cheap so we choose to stick with the free or nearly free option on our boat (we bought the boat with an older HF Radio and got a Pactor Modem cheaply). If your boat does not already have a HF Radio (Ham or SSB) and a Pactor Modem, then a Satellite phone still might be the least expensive alternative for you. HF Radio and Pactor Modem, new, are rather spendy, but they are not uncommonly found on used boats. So if you have one, learn to use it to get weather downloads.
What is a GRIB file?
GRIB (GRIdded Binary or General Regularly-distributed Information in Binary form) is a concise data format commonly used in meteorology to store historical and forecast weather data.
Warning: GRIB files are raw data, not interpreted and analyzed by humans as a weather forecast is. Although they are useful, they should not be your only source of weather data when offshore.
Using HF Radio to receive weather
There are at least two ways to get weather updates from your radio. One is Weather Fax and the other are GRIB files downloads. Both use Airmail software to download them, read our article about Airmail, Sailmail, and Winlink to know how this will work for you.
To download GRIB files sent over the HF radio using Airmail or other software, you will need to be near shore to get internet, or use a Pactor modem attached to your HF radio. See this article on how to connect your laptop to your HF Radio.
Using your Laptop to view Weather Files
GRIB files on your Laptop Navigation Program
The GRIB files can probably be displayed on your laptop via the navigation program – Coastal Explorer displays the GRIB files (see right) in an overlay over your charts so you can see where you are with respect to the weather forecast. To do this use the Open folder symbol in the Graphical Weather Forecast bar and point to your downloaded file. See more explicit detailed instructions for Weather downloads in Coastal Explorer.
At right is the pressure and wind speed chart for the west coast – wave height, wave direction, wave period, humidity and temperature are also available – simply select the check boxes for the parameter you want to see or hide. Then you can step through the forecast by hours or days to see what is coming. Note that the bright green boat symbol is the actual boat location from the GPS.
Weather Data viewing using Airmail
Airmail has a GRIB file viewer built in, read about Airmail’s Weather Fax Companion, ViewFax.
Weather Fax is displayed in the graphical form shown below. You will need to understand the symbology. If you need a brush-up, the Weather Code and Symbols Legend from Nav Canada is pretty complete.