This image of Hurricane Wilma was generated from data retrieved by the AIRS instrument on October 20, 2005 at 1:30 p.m. EDT. At that time Hurricane Wilma was located 255 km (160 miles) south-southeast of Cozumel, Mexico and was slowly heading towards the Yucatan peninsula at 7 km/h (5 mph). Maximum sustained winds were near 230 km/hr (145 mph), making Wilma a Category 4 hurricane on the Saffir-Simpson Scale.
This false-color image shows how the storm looked through the AIRS 12-micrometer infrared window channel. Window channels measure the temperature of the cloud tops or the surface of the Earth in cloud-free regions. The lowest temperatures in dark purple are associated with high, cold cloud tops that make up the top of the hurricane. The infrared signal does not penetrate through clouds, so the purple color indicates the cool cloud tops of the storm. In cloud-free areas, the infrared signal is retrieved at the Earth's surface, revealing warmer temperatures. Cooler areas are pushing to purple and warmer areas are pushing to red. Green generally indicates the presence of clouds. Notice that some high cold clouds as indicated in the infrared do not show up much in the microwave. Microwaves are strongly affected by rain, so some high clouds are almost certainly not raining and may be pretty thin (like cirrus).
Image and text courtesy of the AIRS Science Team at the NASA Jet Propulsion Laboratory.