The PredictWind weather service is popular with offshore sailors, and with a paid PredictWind subscription weather forecasts and routing can be requested via email including access via Sailmail. Our Airmail software version 3.5.054 onward (from January 2020) streamlines access, but any older version can also provide simple access to PredictWind forecasts. Any method of connection can be used: SSB radio, Iridium or Inmarsat handsets or terminals including the Iridium GO.
The first step is to create an account on the PredictWind website. A free account can be used to access basic weather via the web, but a Standard or Professional subscription is required to request weather via email (or direct with the Iridium GO). Then download and install the PredictWind Offshore app, which is used to both request and display weather data.
Then read the how-to info in the Offshore help menu or on the PredictWind website to set your waypoints, adjust the grib area, and request files. Pay attention to file size, large files are fine via wired or WiFi internet but small files are needed via satellite or radio. And while an unlimited data plan for the Iridium GO avoids unexpected airtime charges, the connection is still pretty slow.
Practice with Offshore via a WiFI connection. Adjust waypoints and the grib area as needed, click “Download” and make the desired selections, then select “Web” and click “Download All”. This will fetch weather directly via the web, great for planning but useless at sea.
To access PredictWind via Sailmail, first create a folder (if not already done) for exchanging requests and data. Do this by opening Windows Explorer, open the “Documents” folder and creating a folder called “PredictWind”. Airmail (from ver 3.5.054) will find this and use it automatically.
To send a request via Sailmail, proceed as above except select “Email” instead of “Web”. Click “Save File” and save the “EmailRequest.pwr” file in the “PredictWind” folder under Documents.
Airmail 3.5.054 automatically creates an outgoing message with the request-file attached. Connect to Sailmail to send the request, wait a few minutes and connect again to retrieve the reply files, which will be saved into the same PredictWind folder. Now go back to Offshore and use the File menu to open the files. Sort by date (click the “Date” column in the file-open box), and select the files that were just retrieved– a “pwu” file and one or more “grb” files. Offshore will show a wind graph, click “Map” to see the grib display.
For earlier Airmail versions, create an address-book entry for “PredictWind” with an address of offshore@predictwind.com. Use this to create a new outgoing message, and then attach the request file using Airmail’s “File” menu and “Attach FIle”. In the file-open box, open the PredictWind folder under “Documents” and select “EmailRequest.pwr”. Connect to Sailmail to send the request, wait a few minutes and connect again to retrieve the reply files. Then open each reply message and copy the attached file to the PredictWind folder under Documents. Then open them from Offshore’s File menu as above.
PW gribs are standard grib files and can be viewed with any viewer including our Viewfax software, and likewise, grib-files from our Saildocs server or other sources can be opened and displayed in PW Offshore using the File/Open menu.
A couple of things to note: The most-often used forecast models for offshore sailing are NOAA’s GFS and the European ECMWF model. These are the same models as available from our Saildocs service. There are endless debates as to which is “better”. In terms of forecast accuracy, ECMWF has higher resolution and probably a slight edge in accuracy, ignoring time. But time is certainly important, earlier advance notice for an unexpected change is always valuable. NOAA runs GFS every 6 hours with data available from Saildocs as early as 4 hours after the synoptic (zero-hour) forecast time. ECMWF runs every 12 hours, with data available about 8 hours after. PW provides GFS only every 12 hours about 9 hours after, and ECMWF about 11 hours after.
And again, pay attention to file size. Large files are terrific for planning when you have wired or WiFi internet, but offshore communications are slow (and expensive for satellite airtime), so small files are needed via satellite or radio.
And remember that if you are using PredictWind from a phone or tablet, you can also access Sailmail via that phone or tablet using your PC as an onboard mailserver with Airmail’s MailServer function.