WeatherTrack an incredibly comprehensive weather app -- it accesses many data models from different agencies and provides worldwide coverage. The GRIB layers include wind, precipitation, have height/direction/period, ocean and tidal currents, air and sea temps, relative humidity and more. WeatherTrack works offline, and GRIB files can be downloaded through an SSB connection, an Iridium AxcessPoint or as an email attachment and opened in the app.
Overall, this app has a ton to offer and will probably require some time to figure out initially, especially if you're a bit of a weather novice, but the amount of data it provides is worth it.
WeatherTrack is available for iPhone and iPad for $4.99 from iTunes