This NOAA satellite image taken Monday, Aug. 20, 2007 at 12:45 PM EDT shows Hurricane Dean. Dean spared the Cayman Islands the worst of its fury on Monday as it headed for a collision course with Mexico's resort-dotted Caribbean coast, sending tourists fleeing for the airports and locals searching for higher ground. Dean was already a powerful Category 4 storm as it raked the Cayman Islands. The U.S. National Hurricane Center said it could grow into a monstrous Category 5 hurricane before slashing across the Yucatan Peninsula and emerging in the oil-rich Gulf of Campeche. Eight people have died so far in the Caribbean. (AP Photo/NOAA)
The ingredients for a hurricane include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist long enough, they can combine to produce the violent winds, incredible waves, torrential rains, and floods we associate with this phenomenon. Each year, an average of ten tropical storms develop over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Many of these remain over the ocean and never impact the U.S. coastline. Six of these storms become hurricanes each year. In an average 3-year period, roughly five hurricanes strike the US coastline, killing approximately 50 to 100 people anywhere from Texas to Maine. Of these, two are typically "major" or "intense" hurricanes (a category 3 or higher storm on the Saffir-Simpson Hurricane Scale). What is a Hurricane? A hurricane is a type of tropical cyclone, which is a generic term for a low pressure system that generally forms in the tropics. The cyclone is accompanied by thunderstorms and, in the Northern Hemisphere, a counterclockwise circulation of winds near the earth's surface. Tropical cyclones are classified as follows: * Sustained winds A 1-minute average wind measured at about 33 ft (10 meters) above the surface. ** 1 knot = 1 nautical mile per hour or 1.15 statute miles per hour. Abbreviated as "kt". Tropical Depression An organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds* of 38 mph (33 kt**) or less Tropical Storm An organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds of 39-73 mph (34-63 kt) Hurricane An intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 mph (64 kt) or higher Hurricanes are categorized according to the strength of their winds using the Saffir-Simpson Hurricane Scale. A Category 1 storm has the lowest wind speeds, while a Category 5 hurricane has the strongest. These are relative terms, because lower category storms can sometimes inflict greater damage than higher category storms, depending on where they strike and the particular hazards they bring. In fact, tropical storms can also produce significant damage and loss of life, mainly due to flooding.