Hurricanes & Tropical Storms

Hurricanes and tropical storms are among nature's most powerful forces because of their size and potential for destruction. Hurricanes are tropical cyclones - the general term for all circulating weather systems over tropical waters. Powered by heat from the sea, they are steered by the upper level winds and by their own sometimes ferocious energy.

Florida has experienced the greatest number of hurricane landfalls of any state in the nation because of its geographic location. Florida's flat topography also makes it susceptible to the full force of hurricane winds and powerful storm surge. Between 1900 and 2006, Florida was impacted by 68 hurricanes, 31 of which were major hurricanes (Category 3 or higher). For more information regarding Florida hurricanes and their frequency, see Profiling Hazard Events, an excerpt from the State of Florida Hazard Mitigation Plan.

The Atlantic Hurricane season lasts from June 1st to November 30th with the peak season from mid-August to late October.

Tropical cyclones are classified as follows:

Tropical Depression: A disturbance with a clearly defined low pressure area; highest wind speed is 38 miles per hour.
Tropical Storm: A distinct low pressure area defined by a counterclockwise rotating circulation with winds of 39 to 73 miles per hour.
Hurricane: Once a tropical storm's constant wind speed reaches 74 mph or greater, it is classified as a hurricane. In the western Pacific, hurricanes are called "typhoons," and similar storms in the Indian Ocean are called "cyclones."

Hurricane Categories and Evacuation Levels

Hurricanes are categorized on a scale of 1 to 5 based on the strength (barometric pressure and wind speed) of the storm. The scale is called the Saffir-Simpson Hurricane Scale. Evacuation zones in coastal counties in Florida are based on the potential storm surge from the threatening hurricane, taking into account its projected strength on the Saffir-Simpson Scale, the expected track (landfalling, parallelling and exiting direction) and forward speed.Hurricane Hazards The hurricane can combine storm surge, powerful winds, tornadoes and torrential rains into a devastating combination.

Saffir-Simpson Hurricane Scale

Category	Sustained Winds	Damage
1	74-95 mph	Minor
2	96-110 mph	Moderate
3	111-130 mph	Major
4	131-155 mph	Severe
5	Above 155 mph	Catastrophic

Hazards

Storm surge is an abnormal rise in sea level 50 to 100 miles wide that sweeps across the coast near where the "eye" of the hurricane makes landfall. The surge of high water, topped by waves, can be devastating. The stronger the hurricane winds and the shallower the offshore water, the higher the surge will be. Along the immediate coast, storm surge is the greatest threat to life and property.
Hurricane-force winds, 74 mph or more, can destroy buildings and mobile homes. Debris can become flying missiles in hurricanes. Winds often stay above hurricane strength well inland. Even if your building is located outside of the coastal flood areas, it is extremely important to secure your facility before the storm.
Widespread torrential rains, often in excess of 10 inches can produce destructive floods. This is a major threat to areas well inland. If your business is located in the 100-year flood prone area, it is extremely important that you have flood insurance, floodproof your facility to the extent feasible and have a plan to evacuate or move your operations, if necessary.
Hurricanes also produce tornadoes, which add to the hurricane's destructive power.

Warnings & Advisories

As with all hazardous weather, it is important to keep informed and know the difference between "watches" and "warnings."

Tropical Storm Watch - An alert for a specific area that a tropical storm may pose a threat within 36 hours.
Tropical Storm Warning - An alert that tropical storm conditions, including sustained winds of 39 to 73 mph, are expected in specific areas within 24 hours.
Hurricane Watch An alert for a specific area that hurricane conditions pose a threat within 36 hours.
Hurricane Warning - An alert that hurricane conditions are expected in a specified coastal area within 24 hours. All precautions should be completed immediately.
Evacuation Order - The most important instruction you will receive. Once issued, an evacuation order is mandatory.

Inland/Freshwater Flooding from Hurricanes

Hurricanes can produce widespread torrential rains. Floods are the deadly and destructive result. Flash flooding can occur due to the intense rainfall. Flooding on rivers and streams may persist for several days or more after the storm. The speed of the storm and the geography beneath the storm are the primary factors regarding the amount of rain produced. Slow moving storms and tropical storms tend to produce more rain. Between 1970 and 1999, more people lost their lives from freshwater flooding associated with landfalling tropical cyclones than from any other weather hazard related to tropical cyclones. See the "Flooding" section for more specific information on flood related emergencies.

Determining your vulnerability to storm surge, freshwater flooding and high winds is critical in the development of your Business Continuity Plan. Evacuation or potential long-term structural damage and/or inaccessibility to your facility means you need to develop a crisis communication plan for your employees, clients or customers; develop a mitigation plan to reduce the physical damage to your facility or equipment and be prepared to identify an alternate workplace(s) to continue essential business operations. A website has been developed by the State of Florida, Division of Emergency Management (www.floridadisaster.org). This site will guide you toward the state and local information for your area.