Seeing two winds charts is like getting a second opinion. If there is consensus between the forecast models there is a higher degree of confidence those conditions will prevail.
The BOM and GFS models are independent. They are produced by different agencies and have different model physics so when they arrive at the same conclusion you can be more confident the forecast will be correct.
If the models differ on any given day and one says strong winds while the other says low winds then there is little consensus and therefor lower confidence in an accurate forecast on that day.
The BoM model is the model we have always used and is the model used by Meteye and Willyweather. GFS is the model used by many other weather sites including Windfinder, Buoyweather, Windy, WindGuru and others. In most parts of Australia the BoM model will be more accurate but there some areas where GFS may prove more reliable. Users should observe both over a period of time and determine which performs better at their location.
Technical Information
The BoM (ADFD) model has a resolution of 3km in VIC & TAS and 6km in other states, it covers Australia out to a distance of 60nm from shore. The GFS model has a resolution of 13km and covers the entire globe.
Note: In June 2019, thanks to a 10 fold increase in computing power, NOAA who produce the GFS upgraded the model to a high performance FV3 version. FV3 is the version used by Fish Ranger.
Wondering why we don't we use the ECMWF 9km model? The BOM model is based on the 'EC' model so they have very similar model physics and are not independent. By showing BOM and GFS models we can present two high quality independent forecasts.
We use bilinear interpolation to provide forecasts true to the chosen location, be they on sea or land.