IMPORTANT TROPICAL TERMS
- Tropical Cyclone – A general term used to describe a tropical depression, tropical storm, or hurricane.
- Tropical Disturbance – A poorly organized cluster of thunderstorms that usually has no closed surface circulation.
- Tropical Depression – A cluster of thunderstorms organized around a central circulation with surface winds of 38 mph or less.
- Tropical Storm – A cluster of thunderstorms with a substantial rotary circulation and sustained winds of 39-73 mph. It is at this stage of development that the storm is assigned a name.
- Hurricane – A severe tropical cyclone that is nature’s most powerful storm, with sustained winds of 74 mph or greater.
- Hurricane/Tropical Storm Watch – Hurricane or Tropical Storm conditions are possible in the watch area within 36 hours.
- Hurricane/Tropical Storm Warning – Hurricane or Tropical Storm conditions are expected in the warning area within 24 hours.
WHAT IS A HURRICANE?
- A hurricane is a fierce storm with strong winds rotating around a moving center of low atmospheric pressure.
- Hurricanes rotate counter-clockwise in the northern hemisphere.
- Maximum wind speeds must be 73 miles per hour or more. Once winds go below 73 miles per hour, it is a tropical storm.
- The word hurricane is regional — applying to tropical cyclones in the north Atlantic Ocean, parts of the northeast Pacific Ocean and parts of the south Pacific Ocean.
- A typhoon is the same thing occurring in the northwest Pacific Ocean.
- Hurricane season lasts June 1 through November 30. It is rare, but hurricanes have formed in the Atlantic as early as March or as late as December.
WHERE DO THEY USUALLY HIT?
- 36% of all U.S. hurricanes hit Florida.
- 76% of Category 4 or higher hurricanes hit Florida or Texas.
HOW MANY CATEGORY FOUR AND FIVE STORMS HAVE HIT?
- Since 1900, just three Category 5 storms have hit the continental U.S. There have been 15 Category 4 storms in that time, including Hurricane Charley.
- The last time the U.S. was hit by two hurricanes of Category 4 or above in the same year was 1915. That year a Category 4 storm hit Galveston and another one hit New Orleans.
- Category 5 storms since 1900 (in order of intensity): 1) Unnamed storm hit Florida Keys in 1935, killing 408 people, 2) Hurricane Camille hit Mississippi in 1969, and 3) Hurricane Andrew hit southeast Florida in 1992.
HURRICANE CATEGORIES – The categories are determined by the Saffir-Simpson Scale.
CATEGORY ONE: winds 74-95 mph (64-82 kt or 119-153 km/hr).
- Storm surge 4-5 feet above normal.
- No real damage to buildings or structures.
- Shrubs, loose signs and unanchored mobile homes may sustain some damage. Coastal flooding is possible.
CATEGORY TWO: winds 96-110 mph (83-95 kt or 154-177 km/hr).
- Storm surge 6-8 feet above normal.
- Considerable damage to shrubbery and trees as well as to mobile homes, poorly constructed signs and piers.
- Coastal and low-lying escape routes flood 2-4 hours before arrival of the hurricane center.
- Example: Hurricane Bonnie hit the North Carolina coast in 1998.
CATEGORY THREE: winds 111-129 mph (96-112 kt or 178-208 km/hr).
- Storm surge generally 9-12 ft above normal. Some damage to small residences.
- Some large trees blown down. Some mobile homes and poorly constructed signs are destroyed.
- Flooding near the coast destroys smaller structures.
- Terrain lower than 5 ft above sea level may be flooded inland 8 miles (13 km) or more.
- Example: Hurricane Fran hit North Carolina in 1996.
CATEGORY FOUR: winds 130-156 mph (113-136 kt or 209-251 km/hr).
- Storm surge generally 13-18 ft above normal.
- Roofs destroyed on buildings and residences, Shrubs, trees, and signs blown down. Destruction of mobile homes. Extensive doors & window damage.
- Terrain lower than 10 ft above sea level may be flooded.
- Example: Hurricane Luis passed over the Leeward Islands in 1995.
CATEGORY FIVE: winds greater than 157 mph (137 kt or 252 km/hr).
- Storm surge generally greater than 18 ft above normal.
- Complete roof failure on many residences and industrial buildings. Some buildings completely destroyed. All shrubs, trees, and signs blown down.
- Complete destruction of mobile homes.
- Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline.
- Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the shoreline may be required.
- Example: Hurricane Andrew hit Florida in 1992.
(Source: Associated Press)