There is a current thread on the weather routing software being used by Tote aboard the El Faro here - If You Don’t Trust the NWS You Sure Can’t Trust Applied Weather Technology -
The software basically models the ship’s behavior (speed, motion, fuel consumption) based on the ship’s characteristics (horsepower, displacement, draft, LOA) and environmental factors (current, wind, waves, swell). The software I’ve seen will on demand generate minimum time or minimum fuel routes within the sea height, wind speed limits.
I don’t know what type of files the routing company uses to download the weather data from the weather services but what is sent to the ship is a package of files, no GRIB files as far as I know,