The GFS 850mb vorticity was added this past weekend to the GFS Tropical menus. The 850mb vorticity can be a potential early indicator of tropical cyclone genesis.

http://hp2.wright-weather.com/avn-tropical.shtml

The 850mb vorticity parameter has already been part of the ECMWF model guidance for a number of years.

http://hp2.wright-weather.com/ecmwf.shtml