City of Fort Lauderdale - Hurricane Preparedness - What is a Hurricane?
City of Fort Lauderdale - Hurricane Preparedness
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Hurricanes - Basic Information

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.

Hurricane Image

Tropical cyclones are classified as follows:

  • Tropical Depression - An organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of 38 mph or less.
  • Tropical Storm - An organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds of 39-73 mph.
  • Hurricane - An intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 mph or higher.

Hurricane Terms

Photo of Storm DamageThe Hurricane Season - The portion of the year having a relatively high incidence of hurricanes. The hurricane season in the Atlantic, Caribbean, and Gulf of Mexico runs from June 1 to November 30.

Saffir-Simpson Hurricane Scale - 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.

Tropical Storm - winds 39-73 mph
Category 1 Hurricane - winds 74-95 mph
Category 2 Hurricane - winds 96-110 mph
Category 3 Hurricane - winds 111-130 mph
Category 4 Hurricane - winds 131-155 mph
Category 5 Hurricane - winds 156 mph and up

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

Hurricane Warning - A warning that is issued when hurricane conditions -- sustained winds of 74 mph or higher -- 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.

Tropical Storm Watch - An announcement that a tropical storm or tropical storm conditions pose a threat to coastal areas generally within 36 hours.

Tropical Storm Warning - A warning that sustained winds within the range of 39 to 73 mph associated with a tropical storm are expected in a specified coastal area within 24 hours or less.

Tornado Watch - An announcement issued when conditions are favorable for the development of tornadoes in and close to the watch area.  Their size can vary depending on the weather situation.  They are usually issued for a duration of 4 to 8 hours.  They normally are issued well in advance of the actual occurrence of severe weather.  During the watch, people should review tornado safety rules and be prepared to move a place of safety if threatening weather approaches.

Tornado Warning - An announcement issued when a tornado is indicated by radar or sighted by spotters; therefore, people in the affected area should seek safe shelter immediately.  Tornado Warnings can be issued with or without a Tornado Watch already being in effect.  Tornado Warnings are usually issued for a duration of approximately 30 minutes.

Flood / Flash Flood Watch - An announcement to inform the public that current and developing conditions are favorable for flooding or flash flooding in and close to the watch area, but the occurrence is neither certain nor imminent.

Flood / Flash Flood Warning - A warning issued to inform the public that flooding or flash flooding is in progress, imminent, or highly likely in the affected area.