Hurricane Katrina, which struck New Orleans and other Gulf Coast communities on August 29, 2005, provided the worst kind of reminder of the importance of accurate hurricane prediction — and of heeding those predictions. This video segment adapted from NOVA scienceNOW a year before Katrina struck, describes the current state of research into what causes hurricanes and how scientists are now able to "see" inside the storms in their ongoing efforts to more accurately predict both the path and intensity of these powerful storms.
Tropical cyclones are the most powerful weather events on Earth. These storms, also known as hurricanes and typhoons, depending on where they form, produce sustained winds of at least 119 kilometers (74 miles) per hour. They can dump rain at a rate of more than three centimeters (1.2 inches) per hour and trigger sudden, unpredictable surges in ocean tides that cause extensive property damage and loss of life. In 2004, for example, Hurricane Jeanne struck the Caribbean nation of Haiti, killing more than 3,000 people and nearly destroying the coastal city of Gonaïves. By late 2005, the death toll from Hurricane Katrina had surpassed 1,300, and property damage estimates had grown to several billion dollars. In an attempt to save lives and mitigate damage caused by hurricanes, scientists have gone to great lengths to better understand these storms.
Hurricanes originate over warm tropical oceans. It is the heat of the water that provides the developing storm's energy. In fact, water that is less than 27°C (80°F) does not possess sufficient heat to generate and sustain a hurricane.
A hurricane begins when winds blowing across the surface of the warm ocean water form clusters of strong thunderstorms known as tropical disturbances or tropical waves. The warm water fuels these thunderstorms, causing them to rise. As they do so, they draw water vapor off the ocean surface. When the rising air cools, the water vapor condenses to form clouds, a process that releases heat. This heat warms the center, or eye, of the storm, causing more surface water to evaporate. Meteorologists call this cycle a "heat engine." As long as a storm has access to warm ocean water, this engine will continue to drive the hurricane's growth.
Since the early 1990s, some of the most important advances in hurricane research have been in satellite imagery. Today, satellites use infrared and microwave imagers to record air temperature and humidity, as well as the surface temperature of tropical oceans where hurricanes form. Satellite altimeters measure ocean surface height, helping scientists determine the locations of high-energy swells. In addition, satellite radar now allows scientists to observe the intensity of thunderstorms that form inside hurricanes. These storms, called "hot towers," may reach heights of 14.5 kilometers (9 miles) above the ocean surface. Scientists have found that the presence of hot towers in a developing tropical storm indicates a high probability that the storm will intensify into a hurricane within hours.
Model how wetlands reduce the intensity of a hurricane in this NOVA scienceNOW classroom activity.
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