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Hurricanes

Hurricanes

Hurricanes | Get a Hurricane Kit | Make a Plan | Prepare | During the Storm | After the Storm


hur·ri·cane

tropical cyclone with winds of 74 miles per hour or greater that occurs especially in the western Atlantic, usually accompanied by rain, thunder, and lightning, and that sometimes moves into temperate latitudes

Hurricanes have earned their reputation as destroyers. The word "hurricane" itself actually derives from "Hurakan," a destructive Mayan god. If you have ever had your life impacted by a hurricane, you understand the power the contain. They are severe tropical storms that form in the southern Atlantic Ocean, Caribbean Sea, Gulf of Mexico and in the eastern Pacific Ocean. People who live in coastal communities should plan what they will do if they are told to evacuate. Evaporation from the seawater increases their power.

Hurricanes rotate in a counter-clockwise direction around an "eye." They have winds at least 74 miles per hour. The can deliver massive downpours of rain. Some larger or slower moving storms can dump dozens of inches of rain in a short amount of time. This can create flooding in areas in the path of the Hurricane. They also bring high sustained winds along as they come ashore. This can damage structures, trees, cars and more. The prevailing winds of a hurricane pushes a wall of water, called a storm surge, in front of it. This wall of water can be especially dangerous if it coincides with high tide. It can cause major beach erosion and inland flooding. And if that wasn't enough, Tornadoes are often spawned by hurricanes as they come ashore.

Hurricane damage depends no only on the strength of the storm but on how it makes contact with land. If the storm only grazes the coastline, we are spared from full power of the hurricane. The damage will also depend on whether the left or right side of the hurricane strikes. The right side of a hurricane is more powerful because the wind speed and hurricane's speed of motion complement each other. Keep in mind that damage isn't restricted to the coast. Significant damage can be done to cities and towns far from the coast. In 1996, Hurricane Fran swept 150 miles (241 km) inland to Raleigh, N.C. The damage included down trees, destroyed homes and in some cases power was out in some areas for weeks. The total damage was i the billions of dollars.

How does a Hurricane form?

Hurricanes develop in warm, tropical regions where the water is at least 80 degrees Fahrenheit (27 degrees Celsius). To form, the storms require moist air and converging equatorial winds. Most Atlantic hurricanes begin off the west coast of Africa as thunderstorms that move out to sea over the warm, tropical ocean waters.

The eye is the hurricane's low-pressure center. The eye is relatively calm and surrounded by a wall, the eye wall, where the storm's most violent winds are found. Rain bands circle the eye outward consist of thunderstorms and play a key role in the evaporation and condensation cycle the that feeds the hurricane.

Hurricanes begin as clusters of clouds and thunderstorms called a Tropical Disturbances. These are low-pressure areas that feature little or no rotation. Most tropical disturbances die out but others develop into hurricanes. In these cases, the thunderstorms in the tropical disturbance release latent heat which warms the area. This causes the air density to lower, dropping the surface pressure. The wind speeds then increase as cooler air rushes underneath the rising warm air. The disturbance begins to rotate due to the Coriolis force, a natural phenomenon, that causes fluids and free-moving objects to veer to the right of their destination in the Northern Hemisphere and to the left in the Southern Hemisphere. The incoming wind from the rotation bring in more moisture which condenses to form more cloud activity and then releases more heat as the cycle of strengthen begins.

Life Cycle of a Hurricane

Due to the massive amount of destruction a hurricane can bring, it's easy to compare it to a kind of monster. It may not be a living organism but it does require substance to grow and strengthen. It a tropical disturbance continues to find enough warm, moist air along with optimal wind and pressure conditions, it will continue to grow and develop.

Hurricanes can develop within hours or some may take up to several days to develop. They are classified into three stages:

  1. Tropical depression: wind speeds of less than 38 mph
  2. Tropical storm: wind speeds of 39 to 73 mph
  3. Hurricane: wind speeds greater than 74 mph

Hurricanes vary in physical size. Some may be compact with only a few bands of wind and rain while others may be large and spread over hundreds or thousands of miles. Once a hurricane has formed and intensified, it will eventually encounter conditions that deny it the warm moist air it requires. If a hurricane moves onto cooler waters, pressure will decrease and winds slow until the storm dissipates. Making landfall will also weaken a hurricane The lack of warm moist air vanishes and the friction of an uneven landscape decreases the wind speeds will eventually eliminate the large pressure difference that fuels the storm.

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Hurricane Categories

Hurricanes can unleash incredible damage when they hit. With enough advance warning though, cities and coastal areas can give residents the time they need to fortify the area and even evacuate. To better classify each hurricane and prepare those affected for the intensity of the storm, meteorologists rely on rating systems.

Hurricanes are rated based on the Saffir-Simpson Hurricane Scale . This scale was developed in the early 1970s by Herbert Saffir and Dr. Robert Simpson. The scale, based on wind speeds, estimates barometric pressure and storm surge associated with each category. It is used to give an estimate of flooding and expected damage if a hurricane makes landfall.

Category 1 - Minimal
Winds: 74 - 95 mph or 64 - 82 kts
Surge: 4 - 5 feet
Central Pressure: greater than 980 mb or 28.94 in

  • Some coastal road flooding and minor pier damage.
  • Damage primarily restricted to shrubbery, trees, and unanchored mobile homes
  • No substantial damage to other structures
  • Some damage to poorly constructed signs.

Category 2 - Moderate
Winds: 96 - 110 mph or 83 - 95 kts
Surge: 6 - 8 feet
Central Pressure: 965 - 979 mb or 28.50 - 28.91 in

  • Considerable damage to shrubbery and tree foliage, some trees blown down
  • Major damage to exposed mobile homes
  • Extensive damage to poorly constructed signs
  • Some damage to windows, doors and roofing materials of buildings, but no major destruction to buildings.
  • Coastal roads and low-lying escape routes inland cut off by rising water about two to four hours before landfall
  • Considerable damage to piers
  • Marinas flooded
  • Small craft in protected anchorage torn from moorings

Category 3 - Extensive
Winds: 111 - 130 mph or 96 - 113 kts
Surge: 9 - 12 feet
Central Pressure: 945 - 964 mb or 27.91 - 28.47 in

  • Foliage torn from trees and large trees blown down
  • Poorly constructed signs blown down
  • Some damage to roofing, windows, and doors
  • Some structural damage to small buildings
  • Mobile homes destroyed.
  • Serious flooding along the coast
  • Many small structures near the coast destroyed
  • Larger coastal structures damaged by battering waves and floating debris
  • Low-lying escape routes inland cut off by rising water about three to five hours before landfall
  • Flat terrain 5 feet or less above sea level flooded up to 8 or more miles inland.
  • Evacuation of low-lying residences within several blocks of shoreline may be required.

Category 4 - Extreme
Winds: 131 - 155 mph or 114 - 135 kts
Surge: 13 - 18 feet
Central Pressure: 920 - 944 mb or 27.17 - 27.88 in

  • Shrubs, trees, and all signs blown down
  • Extensive damage to roofs, windows, and doors, with complete failure of roofs on many smaller residences
  • Mobile homes demolished
  • Flat terrain 10 feet or less above sea level flooded inland as far as 6 miles
  • Flooding and battering by waves and floating debris cause major damage to lower floors of structures near the shore
  • Low-lying escape routes inland cut off by rising water about three to five hours before landfall
  • Major erosion of beaches
  • Massive evacuation of inland residences as far inland as 6 miles may be required.

Category 5 - Catastrophic
Winds: greater than 155 mph or 135 kts
Surge: greater than 18 feet
Central Pressure: less than 920 mb or 27.17 in

  • Trees, shrubs, and all signs blown down
  • Considerable damage to roofs of buildings, with very severe and extensive damage to windows and doors
  • Complete failure on many roofs of residences and industrial buildings
  • Extensive shattering of glass in windows and doors
  • Complete buildings destroyed
  • Small buildings overturned or blown away
  • Mobile homes demolished
  • Major damage to lower floors of all structures less than 15 feet above sea level within 1500 feet of the shore
  • Low-lying escape routes inland cut off by rising water about three to five hours before landfall
  • Major erosion of beaches
  • Massive evacuation of residential areas on low ground as far inland as 10 miles may be required.

[Information from The National Hurricane Center]

Hurricane Myths and Facts

MYTH: It is safe to go outside during the "eye" of the hurricane.
FACT: It is not safe to go outside during the "eye" of the hurricane. You have no way of knowing how long the light winds will last. Strong winds will return very quickly from the opposite direction. STAY INDOORS.

MYTH: Taping Windows will help prevent breakage and damage.
FACT:Taping does not prevent windows from breaking and takes critical time from more effective preparedness measures. All tape does is help prevent broken glass from scattering inside your home. Window shutters made of 5/8" plywood or metal and fastened correctly can improve the chances of having your home survive the impact of a storm.

MYTH:Water stored in bathtubs and sinks is a good source of drinking water if the public water supply is interrupted or contaminated.
FACT:Water stored in bathtubs and sinks should never be used for drinking or for bathing young children. You can use water stored in bathtubs and sinks for tasks such as flushing the toilet or washing the floor or clothing. Over time, lead can leach from the glaze in bathtubs and sinks into water stored in them.

MYTH: Hurricanes/tropical storms strike only during the official hurricane season of June 1 through November 30.
FACT:Hurricanes/tropical storms sometimes occur before or after the hurricane season. Tropical Storm Anna happened in April 2003. Hurricane Lili occurred in late December 1984. As late as January 2006, Hurricane Zeta (though no threat to land) loomed in the Atlantic Ocean.

MYTH: Opening the windows on the side opposite the wind will relieve the air pressure and not explode my house.
FACT: The best way to keep your home safe is to keep the wind OUT! Studies have shown that opening a window can increase the amount of damage done by wind. When a hurricane threatens, keep your home sealed up tight.

SOME FACTS

  • The first time anyone flew into a hurricane happened in 1943 in the middle of World War II.
  • Hurricanes are the only weather disasters that have been given their own names.
  • All hurricanes begin life in a warm moist atmosphere over tropical ocean waters.
  • The most violent winds and heaviest rains take place in the eye wall, the ring of clouds and thunderstorms closely surrounding the eye.
  • The first hurricane of the year is given a name beginning with the letter "A".
  • The planet Jupiter has a hurricane which has been going on for over 300 years. It can be seen as a red spot on the planet. This hurricane on Jupiter is bigger than the Earth itself.
  • Hurricanes didn't start having boys' names until 1979.
  • In 1967, a hurricane in Texas caused more than 140 twisters.
  • In 1989, Hurricane Hugo completely destroyed several forests in South Carolina.
  • When a hurricane is especially devastating, its name is permanently retired and another name replaces it.

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