Whilst racing, weather data or services such as routing that are not free of charge or easily available to all boats are not allowed by Rule 41(c) (outside help) of the RRS. See Case 120 in the Case book. However, Case 120 clarifies that rule 41c may be changed for any particular race by the notice of race and sailing instructions.
What we use ...
Weather Maps and observations
It isn't all about Grib files - weather maps, satellite images and observations are at least as important.
From MyImage, observations in Expedition or Squid.
Another very good service is SailFlow.
The best data is almost always that from your local government weather agency. They have more resources and data so should have better products.
Most data is available from Expedition, Saildocs or Great Circle/Squid.
These are what we use:
US. Available from Expedition, Saildocs or Squid. Expedition has higher resolution hourly data, but Saildocs is available earlier.
German. Available from Expedition or Squid.
Canadian. Available from Expedition.
Invariably nested inside global or larger regional models.
The best model for Australia, available by subscription from the BOM.
The best model for French waters. Available from Meteo France, Squid or link below.
HIRLAM & Harmonie
European waters. FMI, KNMI, SMHI and YR.no, available from Squid & MyGrib in Expedition or SMHI link below.
ICON EU & CosmoDE
German. A lot of people like these. Available from Squid or MyGrib in Expedition.
HRRR & NAM
Very good models for the US and Caribbean. Available from Saildocs and Squid.
WRF models are almost a dime-a-dozen, but they can be very good.
The Expedition WRF is one of the best of course.
RTOFS - Global, available from Saildocs and Squid.
MyOcean - Europe, available from Squid.
WW3 - waves
Expedition contains current models for various areas.
Tidetech also provides various current products.
Expedition integrated weather & oceanographic data
Expedition eGribs - GFS, ICON, GDPS and high resolution WRF models
Saildocs - GFS, WW3, NAVGEM, COAMPS & RTOFS
KNMI - Hirlam
NOAA GLERL - Great Lakes winds & currents
Norwegian weather office - Weather forecast from Yr, delivered by the Norwegian Meteorological Institute and NRK
OpenSkiron & OpenGrib
Other weather & oceanographic grib data
DWD - OpenData, COSMO & ICON
ECMWF, reanalysis & ERA Interim
Meteo France - Arpege & Arome
NOAA, RTOFS, WW3, Reanalysis, Degrib
SailFlow or SailFlow
Sailing Weather Service
Weather 4D Arome