A hurricane is a type of tropical cyclone, the generic term for a low-pressure system that generally forms in the tropics. Hurricanes are defined as an organized rotating weather system that has sustained winds of 74 mph or greater. Hurricanes are one of nature’s most widespread and destructive weather events. If the cyclone’s wind speeds are between 30 mph and 73 mph it is considered to be a tropical storm. While generally less dangerous than hurricanes, tropical storms still can be deadly.
All tropical cyclones need warm oceans, moisture and light winds above them. If the right conditions last long enough, these tropical cyclones can become hurricanes, producing violent winds, incredible waves, torrential rains and floods. In the Northern Hemisphere, the winds of a hurricane blow in a large counterclockwise spiral around the ‘’eye’’—the storm’s relatively calm center. The width of the eye is generally 20 to 40 miles wide. The diameter of the storm could be as large as 300 miles. Seen from outer space, the overall size of a hurricane can be quite impressive, and some hurricanes have been larger than the entire state of Louisiana. Hurricanes can last for as longs two weeks. During that period, a storm may have impacted thousands of miles ranging from off the coast of Africa to the entire length of the eastern U.S. seaboard.
Hurricanes and the U.S. Coastline
On average, ten tropical storms develop over the Atlantic Ocean, the Gulf of Mexico or the Caribbean Sea each year. The majority of these storms stay over the open ocean and never make landfall. Still, the United States experiences five hurricanes on average every three years. Of these five, two are major hurricanes, category 3 or higher, obtaining speeds of at least 110 mph.
NOAA & NWS
Most of the information contained on the website about hurricanes is courtesy of the National Oceanic and Atmospheric Administration (NOAA) and the National Weather Service (NWS).
In the Atlantic, Caribbean, Gulf of Mexico and the Eastern Pacific, the NOAA National Hurricane Center issues tropical cyclone warnings, watches, advisories, discussions and statements for tropical cyclones. The National Centers for Environmental Prediction Hydrometeorological Prediction Center (NCEP HPC) provides back-up for the National Hurricane Center.
In the Central Pacific, the NOAA Central Pacific Hurricane Center issues tropical cyclone warnings, watches, advisories, discussions and statements for all tropical cyclones in the Central Pacific from 140 degrees west longitude to the International Dateline.
The National Hurricane Center (NHC) is located in Miami, Florida. The NHC’s mission is to save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts, and analyses of hazardous tropical weather and by increasing understanding of these hazards. The NHC vision is to be America’s calm, clear, and trusted voice in the eye of the storm and, with its partners, enable communities to be safe from tropical weather threats. For more information on the NHC see http://www.nhc.noaa.gov/aboutintro.shtml
What Damage Can A Hurricane Cause
Residents of coastal states know all to well the death and destruction that can be caused by a Hurricane. Long before Hurricane Katrina became a household name, the U.S. had experienced significant loss to life and property from hurricanes. Hurricanes such as Andrew, Floyd and Camille killed thousands and caused billions of dollars in damages.
Winds from a hurricane can damage, even flatten residences and businesses and cause the loss of lives and billions of dollars in damages. Hurricanes often cause flooding and not just on the coast. The storms often cause inland, urban and river flooding. In mountainous regions, mudslides can occur. Most deaths from a hurricane are from flooding. The greatest threat, however, is often the storm surge. The National Weather Service says if the surge occurs near high tide, a dome of ocean water of more than 25 feet is possible. The surge can be 50 to 100 miles long.
The Saffir-Simpson Scale
In order to gauge the potential damage from a hurricane, the Saffir-Simpson Hurricane Scale was developed. The Saffir-Simpson Hurricane Scale gives an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline, in the landfall region. Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for loss of life and damage. Category 1 and 2 storms are still very dangerous and warrant preventative measures.
The Five Types of Hurricanes On The Saffir-Simpson Scale.
Category 1—Winds of 74 mph to 95 mph
Minimal Damage – Key Characteristics: Building structures usually receive no significant damage. Low- lying coastal roads may become flooded and there can be damage to shrubbery, trees and unanchored mobile homes. Small boats in exposed anchorages can also be torn from moorings. Recent Category 1 storms include Lili in coastal Louisiana in 2002 and Gaston in 2004 in Central South Carolina.
Category 2—Winds of 96 to 110 mph
Moderate Damage – Key Characteristics: Coastal roads and low-lying escape routes inland are cut off by rising waters two to four hours before the arrival of the hurricane’s center. A category 2 storm generally causes some damage to windows, doors and roofing materials. Mobile homes will likely suffer major damage. Considerable damage to poorly constructed signs, piers, shrubbery and trees with some trees blown down. Hurricane Frances made landfall over Florida in 2004 as a Category 2 storm, and Hurricane Isabel hit the Outer Banks of North Carolina in 2003.
Category 3—Winds of 111 to 130 mph
Extensive Damage – Key Characteristics: Low-lying escape routes are cut off by rising water three to five hours before the hurricane’s center arrives. Mobil homes/trailers are all destroyed. Small buildings, including homes, receive structural damage. Small buildings on the coast are damaged by battering waves and floating debris. In 2004 Hurricanes Jeanne and Ivan made landfall as category 3 hurricanes in Florida and Alabama respectively. In 2005, Hurricane Katrina struck the Gulf Coast as a Category 3 storm.
Category 4—Winds of 131 to 155 mph
Extreme Damage – Key Characteristics: Trees blown down. Complete destruction of mobile homes. Major damage occurs to lower floors of buildings near the shore because of flooding and battering by waves and debris. Roofs collapse on residences. Damage is extensive to windows, doors and roofing materials. Examples of category Four Hurricanes are Hurricane Charley in Florida in 2004 and Hurricane Dennis in Cuba in 2005.
Category Five—Winds of more than 155 mph
Catastrophic Damage – Key Characteristics: Small buildings are overturned or blown away. Extensive shattering of glass in windows and doors ensues. Roofs collapse on many residential and industrial buildings. Category five hurricanes have struck the U.S are the Labor Day Hurricane of 1935 in Florida, Hurricane Camille in 1969 in Mississippi and Hurricane Andrew in Florida in 1992.
A hurricane gains strength by using warm water as fuel. Some scientists predict hurricanes may become stronger because of Earth’s warming climate. However, science dictates that there must be a limit. Kerry Emanuel, a climatologist at the Massachusetts Institute of Technology, found in 1998 that the strongest hurricanes winds occur at approximately 190 mph. He determined this based on the Earth’s ocean and atmospheric conditions at the time.
The Tornado Problem
Hurricane winds can also spawn tornadoes, which may cause more destruction. According to National Oceanic and Atmospheric Administration, tornadoes are most likely to occur in the right-front quadrant of a hurricane. But confusing the matter they can also be embedded in the rain-bands away from the hurricane center.
More than half of the hurricanes reaching landfall spawn at least one tornado. NOAA noted that one study showed that Hurricane Beulah in 1967, which reached landfall in Mexico and Texas, spawned 141 tornadoes.
NOAA says in general tornadoes developed from hurricanes are less intense than the tornados that impact the Great Plains. Still, combing tornadoes with hurricane-force winds can produce substantial damage. There is no way to predict at present which hurricanes will spawn tornadoes or their touchdown.
Hurricane Advisories, Watches and Warnings
When a tropical cyclone gathers enough strength to be considered a threat, NOAA issues an announcement (or series of announcements) to make you aware of the impending storm.
Tropical Storm Watch: An announcement for specific coastal areas that tropical storm conditions are possible within 36 hours.
Tropical Storm Warning: A warning that sustained winds within the range of 34-63kt (39-73 mph or 63-118 km/hr) associated with a tropical cyclone are expected in a specified coastal area within 24 hours or less.
Hurricane Advisory: Advisories are issued at six-hour intervals and describe the path and intensity of the storm. Also included in the advisories are the storms name and its eye position.
Hurricane Watch: An announcement for specific regions that hurricane conditions are possible within 36 hours. If the watch covers the area where you live or work, it is important to listen for further advisories and to be prepared to act quickly if more severe weather updates are issued. This watch should trigger your family’s disaster plan, and protective measures should be initiated, especially those actions that require extra time such as securing a boat, leaving a barrier island, etc.
Hurricane Warning: A hurricane warning is issued when hurricane force winds (74+ mph) are expected to occur within the next 24 hours or less. Once this warning has been issued, your family should be in the process of completing protective actions and deciding the safest location to be during the storm.
Local emergency management officials will be issuing their own bulletins as to whether should evacuate at this time. The Red Cross says you should be completing your storm preparations at this time.
If you don’t evacuate, stay indoors, away from windows, unless you are told otherwise by officials.