Radial velocities are the component of a current in the radial direction, that is directly towards or away from the place of measurement.   In terms of surface current radar,  the radar measures waves coming towards or away from the radar at a particular azimuth, and subtracts the theoretical deep water wave speed.  This basically results in the radial velocity maps linked below.  As the maps are generated on the fly they may take a few moments to load.

Duck Radials | Hatteras Radials