Weather radars can sense clouds and moisture in the air. They do this by sending out strong pulses of energy and then "listening" to the patterns of reflected energy. The radar's computer then creates a picture showing the locations of clouds and moisture.
When a bunch of pictures are captured over a period of time and played back, the radar "movie" lets you see how storms move and change over time.
This radar movie shows the rainbands and eyewall of Hurricane Erin as they swirl around its eye. Blue and green colors are used for places where the rain is light. Yellow, orange, and red colors show areas where the rain is very heavy.