Saturday, May 21, 2005

Storm Terminology for You

Source: Sarasota Herald-Tribune

Hurricane: A storm with sustained winds of at least 74 mph blowing counterclockwise around a calm center of low pressure. Wind gusts may exceed the sustained winds by 25 to 50 percent. Hurricanes are rated by their wind speed, with a Category 1 being the weakest hurricane (74 to 95 mph) and Category 5 being the most intense (over 155 mph). Hurricanes also can generate tornadoes of 150 to 300 mph (Page 26).

Hurricane warning: A warning means that a hurricane is expected to strike within 24 hours. Residents must be ready to leave if local officials order an evacuation of their area.

Hurricane watch: When a watch is declared, hurricane conditions are possible and may threaten an area within 36 hours. When the watch is announced, the area affected and danger period will be specified. Voluntary evacuations may be encouraged at this stage.

Storm surge: Storm surge can be defined as the abnormal rise in water level caused by wind and pressure forces of a hurricane. It can be devastating and in fact is a major cause of damage from hurricanes. The storm surge itself is caused by the wind and pressure "pushing" the water into the continental shelf and onto the coastline. The height of a surge is basically measured as a deviation from the mean sea level in the area, and in some historical storms, this value has reached over 20 feet.

Tropical depression: A low-pressure front with a rotary circulation of clouds and winds up to 39 mph.

Tropical disturbance: A large area of rain and clouds with no circulating winds.

Tropical storm: A storm with a distinct rotation of winds around a center of low pressure with a barometric reading of 29.4 inches or lower. When sustained winds reach 39 mph or higher, the storm is given a name by the National Hurricane Center in Miami.

Rainfall may equal or exceed that of some hurricanes, and tides may be several feet higher than normal. Wind gusts may reach hurricane velocity of 74 mph or more and, depending on tides and other conditions, damage may be just as severe as that caused by a hurricane.

Tropical wave: A weak, low-pressure front moving westward in the trade winds. Clouds and rain are linked to the wave, but it has no wind circulation. May be short-lived or move up to 3,000 miles without change.

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