Tropical Disturbance: A moving area of thunderstorms in the tropics.
Tropical Wave: A westward-moving, low-pressure trough in the deep easterly current that tends to organize low-level circulation. It sometimes travels thousands of miles with little change in shape, producing showers and thunderstorms along its path.
Tropical Depression: An area of low pressure, rotary circulation of clouds and winds up to 38 miles per hour.
Tropical Storm: Counterclockwise circulation of clouds and winds (develops over warm tropical waters) with windspeeds ranging from 39-73 miles per hour. At this stage, the storm is assigned a name.
Hurricane: A tropical storm with windspeeds of 74 miles per hour or more, and dangerously high water and waves.
"Eye" of the Hurricane: The relatively calm area near the center of the storm where winds are light, and the sky often is partly cloudy. The calm area is deceptive because it is bordered by maximum-force winds and torrential rains; it can last from several minutes to more than an hour.
Storm Surge: An abnormal rise in sea level produced by the strong winds and low pressure within a hurricane. The storm surge occurs in the right half of the storm as it makes landfall. The storm surge potentially could elevate sea level from 2-20 feet. (9 out of 10 hurricane-related deaths occur as a result of storm surge rather than winds.) For more information about storm surge, visit
Advisory: Hurricane and storm information delivered to the public every six hours.
Intermediate Advisory: Hurricane and storm information updated every 2-3 hours, or as necessary.
Special Advisory: Hurricane and storm information delivered when there is a significant change in storm-related weather conditions or warnings.
Gale Warning: An advisory that 39-54 mph sustained winds and strong wave action are expected.
Storm Warning: An advisory that 55-73 mph sustained winds and strong wave action are expected.
Hurricane Watch: An announcement of possible hurricane conditions, for a particular area, within 36 hours.
Hurricane Warning: A advisory that a hurricane is expected to strike a specified area within 24 hours or less.