US High-res National Radar from NSSL/U.ofOkla. National high-resolution (1 km) radar reflectivity mosaic, updated once every two minutes. Note that there are no radar sites in the middle of the gulf, so until the storm nears land and the sites that are there, you won't see much on this radar.
Here's a composite I just did which combines both of the dynamic data layers listed above and overlays them on Google Earth.