Homeland Security and Emergency Services

What is a Hurricane?

Hurricanes are one of the deadliest forces of nature, known to generate high winds, torrential rains and tornadoes, and capable of causing death, serious injury and costly property damage. The Atlantic hurricane season runs for six months, from June 1 through November 30.

A hurricane is a type of tropical cyclone, the general term for all circulating weather systems (counterclockwise in the Northern Hemisphere) over tropical waters.

Tropical cyclones are classified as follows:

Tropical Disturbance
A moving area of thunderstorms in the Tropics that maintains its identity for 24 hours or more; a common phenomenon in the tropics

Tropical Depression
An organized system of clouds and thunderstorms with a defined circulation and maximum sustained winds of 38 mph (33 knots) or less

Tropical Storm
An organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 to 73 mph (34-63 knots)

Hurricane
An intense tropical weather system with a well-defined circulation and maximum sustained winds of 74 mph (64 knots) or higher. In the western Pacific, hurricanes are called "typhoons"; similar storms in the Indian Ocean are called "cyclones."

Hurricanes are products of the Tropical Ocean and the atmosphere. Powered by heat from the sea, hurricanes are steered by the easterly trade winds and the temperate westerlies as well as by their own ferocious energy. Around their core, winds grow with great velocity, generating violent seas. Moving ashore, hurricanes sweep the ocean inward, spawning tornadoes and producing torrential rains and floods.

Each year on average, 10 tropical storms (of which six become hurricanes) develop over the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. Many of these remain over the ocean. However, about five hurricanes strike the United States coastline every three years. Of these five, two will usually be major hurricanes (category 3 or greater on the Saffir-Simpson Hurricane Scale).

Terms To Know

By international agreement, Tropical Cyclone is the general term for all cyclone circulations originating over tropical waters, classified by form and intensity as follows:

  • Small Craft Cautionary Statements: when a tropical cyclone threatens a coastal area, small craft operators are advised to remain in port or not to venture into the open sea.
  • Gale Warnings may be issued when winds of 39-54 miles an hour (34-47 knots) are expected.
  • Storm Warnings may be issued when winds of 55-73 miles an hour (48-63 knots) are expected. If a hurricane is expected to strike a coastal area, gale or storm warnings will not usually precede hurricane warnings.
  • Hurricane Watch: issued for a coastal area when there is a threat of hurricane conditions within 24-36 hours.
  • Hurricane Warning: issued when hurricane conditions are expected in a specified coastal area in 24 hours or less. Hurricane conditions include winds of 74 miles an hour (64 knots) and/or dangerously high tides and waves. Actions for protection of life and property should begin immediately when the warning is issued.
  • Flash Flood Watch: flash flooding is possible in the area; stay alert.
  • Flash Flood Warning: flash flooding is imminent; take immediate action.
  • Tornado Warning: spawned by hurricanes, sometimes produce severe damage and casualties; if a tornado is reported in your area, a warning will be issued

Source: U.S. Department of Commerce, NOAA, National Weather Service

Understanding The Warnings

"Hurricane Watch"

A Hurricane Watch means that hurricane conditions MAY threaten an area within 24-36 hours.  When a Hurricane Watch is issued, everyone in that area should listen for further advisories and be prepared to act promptly:

  • Frequently listen to your radio, television or NOAA Weather Radio for official bulletins on the progress of the storm.
  • Fuel and service family vehicles.  Service stations may be unable to pump fuel because of flooding or loss of electrical service.
  • Moor small craft or move to safe shelter.
  • Inspect and secure mobile home tie downs.
  • Tape, board or shutter all window and door openings.  Wedge sliding glass doors to prevent lifting from their tracks.
  • Check for batteries, flashlights and battery-operated radios.
  • Check on your supply of canned food, first aid supplies, drinking water and medications.
  • Secure or bring inside lawn furniture and other loose, lightweight objects, such as garbage cans and garden tools that could become a projectile in high winds.
  • Have on hand an extra supply of cash.

"Hurricane Warning"

A hurricane WARNING is issued when hurricane conditions are expected in a specified coastal area in 24 hours or less.  Hurricane conditions include winds of 74 miles an hour (64 knots) and/or dangerously high tides and waves.  Actions for protection of life and property should begin immediately when the warning is issued, including:

  • Frequently listen to your radio, television or NOAA Weather Radio for official bulletins on the progress of the storm.
  • Complete preparation activities such as putting up storm shutters, storing loose objects, etc.  Move valuables to upper floors.
  • Store drinking water in clean jugs, bottles and cooking utensils.  The water system in your town could become contaminated or damaged by the storm.
  • Check your battery-powered equipment.  Your radio may be your only link with the outside world.  Emergency cooking facilities and flashlights will be essential if utility services are interrupted.
  • Follow instructions issued by local authorities.  Leave IMMEDIATELY if told to do so.
  • Leave low-lying areas that may be swept by high tides or storm waves.
  • If you plan to leave your home, leave early (if possible, in daylight) to avoid the last-minute rush that could leave you stranded.  Stay with friends or relatives, at a low-rise inland hotel/motel, or go to a pre-designated public shelter outside a flood zone.
  • In any case, leave mobile homes for more substantial shelter.
  • Notify neighbors and a family member outside of the warned area of your evacuation plans.
  • Put food and water out for a pet if you cannot take it with you.  Public health regulations do not allow pets in public shelters, nor do most hotels/motels allow them.

Hurricane Scale

All Hurricanes are dangerous, but some are more so than others. The way storm surge, wind and other factors combine determines the destructive power of a hurricane. To make comparisons easier and to make the predicted hazards of approaching hurricanes clearer to emergency forces, hurricane forecasters at the National Oceanic and Atmospheric Administration use a disaster-potential scale which assigns storms to five (5) categories. The Saffir-Simpson Scale can be used to give an estimate of the potential property damage and flooding expected along the coast as a result of hurricane activity.

Saffir-Simpson Hurricane Scale

Category

Wind Speed

Effects

One

74 - 95 mph

No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Also, some coastal road flooding and minor pier damage.

Two

96 - 110 mph

Some roofing material, door, and window damage to buildings. Considerable damage to vegetation, mobile homes, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of center. Small craft in unprotected anchorages break moorings.

Three

111 - 130 mph

Some structural damage to small residences and utility buildings with a minor amount of curtain wall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain continuously lower than 5 feet above sea level (ASL) may be flooded inland 8 miles or more.

Four

131 - 155 mph

More extensive curtain wall failures with some complete roof structure failure on small residences. Major erosion of beach. Major damage to lower floors of structures near the shore. Terrain that is continuously lower than 10 feet ASL may be flooded requiring massive evacuation of residential areas inland as far as 6 miles.

Five

155 mph - ?

Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet ASL and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles of the shoreline may be required.

Source: U.S. Department of Commerce, NOAA, National Weather Service