Emergency Plan Manual

5 HURRICANE BASICS 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 associated 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 anywhere from Texas to Maine. Of these, two two are typically “major” or “intense” hurricanes (a category 3 or higher storm on the Saffir-Simpson Hurricane Scale). What is the 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 Northen Hemisphere, a counterclockwise circulation of winds near the earth’s surface. Tropical cyclone as follows: Tropical Depression *Sustained winds An organized system of clouds and A-1-minute average wind measure at about 33 thunderstorms with a defined circulation and ft (10 meters) above the surface. maximum sustained winds* of 38 mph (33kt** ) or less ** 1 knot = 1 nautical mile per hour. Abbreviated as “kt”. Tropical Storm An organized system of strong thunderstorm with a defined surface circulation and maximun 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.