Warm ocean waters fuel hurricanes, and there was plenty of warm water for Katrina to build up strength once she crossed over Florida and moved into the Gulf of Mexico. This image depicts a 3-day average of actual sea surface temperatures (SSTs) for the Caribbean Sea and the Atlantic Ocean, from August 25-27, 2005. Every area in yellow, orange or red represents 27.8 degrees Celsius (82 degrees Fahrenheit) or above. A hurricane needs SSTs at about this level or warmer to strengthen. The SST data came from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) instrument on NASA's Aqua satellite. AMSR-E was provided to the Aqua program by the Japanese Aerospace Exploration Agency (JAXA). The cloud data came from the GOES satellite, land data from the MODIS instrument on board NASA's Terra satellite.
Click on the link below to view an animation which depicts the sea surface temperatures for the period June 9 through August 29, 2005. Also note the different tracks of Hurricanes Dennis, Emily, and at the very end Katrina.
Images and animation courtesy of the NASA Goddard Space Flight Center Scientific Visualization Studio.