Tropical Storm Dictionary

Florida Keys Hurricane Guide 2009

Barometric Pressure
Barometric pressure is the weight of the column of air that extends from the ground (or water’s surface) to the top of the atmosphere. It is also called air pressure. Air pressure is measured by a barometer. 29.92 is the average air pressure at sea level. Barometric pressure is very low in a hurricane. Labor Day Hurricane: 26.35 inHg(inches of mercury), Georges: 27.68 inHg, Wilma: 26.06 inHg (record low)

Eye
The roughly circular area of comparatively light winds that encompasses the center of a severe tropical cyclone. The eye is either completely or partially surrounded by the eyewall cloud.

Eyewall / Wall Cloud
An organized band or ring of cumulonimbus clouds that surround the eye, or light-wind center of a tropical cyclone. Eyewall and wall cloud are used synonymously.

Hurricane
An intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 MPH (64 knots) or higher.

Hurricane Warning
A warning that sustained winds 64 kt (74 mph or 119 km/hr) or higher associated with a hurricane are expected in a specified coastal area in 24 hours or less. A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continue, even though winds may be less than hurricane force.

Hurricane Watch
An announcement for specific coastal areas that hurricane conditions are possible within 36 hours.

Tropical Cyclone
Tropical cyclones are warm core, non-frontal, low-pressure systems of synoptic scale that develop over tropical or subtropical waters and have a definite organized surface circulation. Tropical depressions, tropical storms, and hurricane are all forms of tropical cyclones, differentiated only be the intensity of the winds associated with them.

Tropical Depression
An organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of 38 MPH (33 knots) or less. Sustained winds are defined as one-minute average wind measured at about 33 ft (10 meters) above the surface.

Tropical Disturbance
A discrete tropical weather system of apparently organized convection—generally 100 to 300 nmi in diameter—originating in the tropics or subtropics, having a nonfrontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field.

Tropical Storm
An organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds of 39–73 MPH (34–63 knots).

Tropical Storm Watch
Hurricane/tropical storm conditions are possible in the specified area, usually within 36 hours. Tune in to NOAA Weather Radio, commercial radio, or television for information.

Tropical Storm Warning
Tropical storm conditions are expected in the specified area, usually within 24 hours.

Storm Surge
An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide and can reach 25 feet high and be 50–1000 miles wide.

Storm Tide
A combination of storm surge and the normal tide (i.e., a 15-foot storm surge combined with a 2-foot normal high tide over the mean sea level created a 17-foot storm tide).