Hurricanes form over tropical waters, encouraged by sea surface temperatures of 26.5 °C (80 °F) or higher. Over such warm waters, hurricanes can explode in size and intensity, becoming Category 4 or 5 storms by the time they make landfall. Like its predecessor Katrina, Hurricane Rita has picked up steam in its trip over a warm Gulf of Mexico. The dark grey circles show measured positions of the hurricane, while lighter grey circles show forecasted positions. Maximum sustained wind speeds at each location are shown in miles per hour (white numbers).
A quartet of satellites, including NASA’s Topex/Poseidon and Jason satellites, have monitored sea surface height during Rita’s journey toward the Gulf Coast. This map results from a combination of data from these satellites collected on September 21, 2005. This image shows ocean circulation patterns in the Gulf of Mexico, framed by the Florida peninsula on the right and the Texas-Mexico Gulf Coast on the left (shown in gray). Red indicates strong circulation of warm waters. Sea surface height is a useful measure of potential hurricane activity because storm-fueling warm water is higher than surrounding cooler water. The area shown in red is approximately 35 to 60 centimeters (roughly 13 to 23 inches) higher than the surrounding Gulf.
A hurricane’s track depends primarily on the winds that steer it, and these winds are forecasted with atmospheric models. The hurricane’s energy source, however, comes from the ocean. Hurricanes travel over both strong ocean currents and smaller currents running in different directions (eddies). As of September 22, 2005, Hurricane Rita was forecasted to continue crossing a circulation feature in the Gulf of Mexico known as the Loop Current, then pass near a warm-water eddy known as the Eddy Vortex. The Eddy Vortex is in the north central Gulf, south of Louisiana.
The Jason satellite carries a radar altitude meter, otherwise known as an altimeter. To determine the ocean’s height, the altimeter measures the time it takes for the microwave pulses to bounce off the surface and return to the spacecraft. This measure, multiplied by the speed of light, gives the range from the satellite to the ocean surface. The joint U.S.-French Topex/Poseidon mission is managed by NASA’s Jet Propulsion Laboratory.