Here is just one web site that will give some light on the subject :- http://www.sea-tech.com/grib.htm
Grib files are very useful, when off shore and away from direct feed into the internet with a computer, where you can access a multitude of weather forecasters .
To receive grib files offshore you will need first - the ability to receive emails - the basic requirements are an HF radio , a modem (known as a Pactor) and a computer - plus relevant software --
Emails at sea can be received if you are a Ham via Winlink or if not via Sailmail or other similar organisations. Check for Info on our CruiserLog WIKI >> go to contents >> Communications lookup : HF Radio and Emails
If you are able to connect directly to the internet, and you need weather for a specific area
, key in :- http://www.cruiserlog.com
and we will give appropriate forecaster URLs.