When you read our blogs or watch our videos, you frequently hear us talking about GRIB files and downloading them. GRIB files is “Greek” to those of you who aren’t bluewater cruising sailors. Since one of our “landlubber” readers asked us to please explain this and make a video – we’ve now done that.
A GRIB file is a data file you can download from the net. It contains raw weather data that you can interpret and use to make your own weather forecast.
GRIB (GRIdded Binary or General Regularly-distributed Information in Binary form
In other words, a GRIB file contains binary information that is displayed over a grid (a grid here is a map of a portion of the world).
GRIB files can contain many different types of data – Vinni and I mostly need wind force and direction and wave height and direction. With those two pieces of information, we can make a reliable weather forecast for the next couple of days. GRIB files are like any weather forecast – generally reliable the first three or four days – thereafter their reliability diminishes rapidly. But even going out two weeks, they can give a general picture of how the weather will develop, which is certainly desirable when sailing a long passage.
As an example, our friends Edd and Judy, who were sailing towards Alaska some years ago, decided to heave to and let a weather front (storm) pass in front of them rather than trying to force their way through. Vinni and I haven’t had to do that yet, although we have slowed down or changed course to let a weather front pass.
We download GRIB files every other day – although sometimes every day if there is heavy weather in sight. Our last passage was 25 days and when it is that long, any weather forecast you take before you leave is hopelessly outdated after the first few days at sea.
There are many places on the net to get GRIB files. When we are in a harbor and there is good internet we use either Predictwind https://www.predictwind.com/ or Windy https://www.windy.com/ for a forecast. Both are excellent, but they need a very good internet connection since the files are big. We don’t have a high-speed connection when we sail – the files we download need to be 10-15 KB (yes – I wrote KB).
We use Sailmail, since we also have our at sea email here. We can’t use our normal gmail since that also needs a mega good internet connection. Sailmail works just fine.
As I noted, we download a GRIB every other day and then spend some time interpreting it. We hope you find the below video instructive – when we were starting out we had to learn all this from scratch – we couldn’t find anything that told us “how to”.