The Saffir-Simpson Hurricane Scale is a 1 to 5 rating based on the hurricane's intensity. This scale estimates potential property damage. Hurricanes or typhoons 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. In the western North Pacific, the term "Super Typhoon" is used for tropical cyclones with sustained winds exceeding 150 mph. For more information on the Saffir-Simpson Hurricane Scale, go to www.nhc.noaa.gov/aboutsshs.shtml.
| Scale Number (Category) |
Sustained Winds (MPH) |
Types of Damage | Hurricanes |
|---|---|---|---|
| 1 | 74-95 | Minimal: Damage primarily to shrubbery, trees, and unanchored mobile homes. No real damage to other structures. | Irene, 1999 |
| 2 | 96-110 | Moderate: Some trees blown down. Major damage to exposed mobile homes. Some damage to roofs, etc. | Georges, 1998 Floyd, 1999 |
| 3 | 111-130 | Extensive: Large trees blown down. Mobile homes destroyed. Some structural damage to small buildings. | Betsy, 1965 Alicia, 1983 |
| 4 | 131-155 | Extreme: Trees blown down. Complete destruction of mobile homes. Extensive damage to buildings. Complete failure of roofs on many small residences. | Hugo, 1989 |
| 5 | >155 | Catastrophic: Complete failure of roofs on many residences and industrial buildings. Extensive damage to windows and doors. Some complete building failure. | Andrew, 1992 |
The term hurricane has its origin in the indigenous religions of old civilizations. The Mayan storm god was named Hunraken. A god considered evil by the Taino people of the Caribbean was called Huracan. Hurricanes may not be considered evil but they are one of nature's most powerful storms. Their potential for loss of life and destruction of property is tremendous.
Those in hurricane-prone areas need to be prepared for hurricanes and tropical storms. Even inland areas, well away from the coastline, can experience destructive winds, tornadoes and floods from tropical storms and hurricanes.
A hurricane is a type of tropical cyclone - an organized rotating weather system that develops in the tropics. Hurricanes rotate counterclockwise in the Northern Hemisphere. Tropical cyclones are classified as follows:
Tropical depressions and tropical storms, while generally less dangerous than hurricanes, still can be deadly. The winds of tropical depressions and tropical storms are usually not the greatest threat. Heavy rains, flooding and severe weather, such as tornadoes, create the greatest threats from tropical storms and depressions.
On average each year, 10 tropical storms, 6 of which become hurricanes, develop in the Atlantic Ocean, Caribbean Sea or Gulf of Mexico. In a typical 3-year span, the U.S. coastline is struck on average five times by hurricanes, two of which will be designated as major hurricanes.
Tropical cyclones are sometimes steered by weak and erratic winds, making forecasting a challenge. Warnings issued from the National Oceanic and Atmospheric Administration's (NOAA) National Hurricane Center and Central Pacific Hurricane Center continue to improve and have greatly diminished hurricane fatalities in the United States.
Despite improved warnings, property damage continues to increase due to growing population on our coastlines. Federal agencies, such as the Federal Emergency Management Agency (FEMA), and organizations such as the American Red Cross, have combined with state and local agencies, rescue and relief organizations, the private sector and the news media to improve preparedness efforts.
Hurricanes are products of a tropical ocean and a warm, moist atmosphere. Powered by heat from the sea, they are typically steered by high-level easterly winds while in the tropics, generally south of 25° north latitude and by high-level westerly winds north of 25° north latitude. When hurricanes become very strong, they can create their own steering winds.
The Atlantic hurricane season starts on June 1. For the United States, the peak hurricane threat exists from mid-August to late October, although the official hurricane season extends through November. Over other parts of the world, such as the western North Pacific, typhoons can occur year-round.
The process by which a disturbance forms and strengthens into a hurricane depends on at least three conditions. First, a disturbance gathers heat and energy through contact with warm ocean waters. Next, added moisture evaporated from the sea surface powers the infant hurricane like a giant heat engine. Third, the hurricane forms a wind pattern near the ocean surface that spirals air inward. Bands of thunderstorms form, allowing the air to warm further and rise higher into the atmosphere. If the winds at these higher levels are relatively light, this structure can remain intact and further strengthen the hurricane.
The center, or eye, of a hurricane is relatively calm with sinking air, light winds and few clouds. The most violent winds and rain take place in the eyewall, the ring of thunderstorms immediately surrounding the eye. At the top of the eyewall (about 50,000 feet), most of the air is propelled outward, increasing the air's upward motion. Some of the air, however, moves inward and sinks into the eye, creating a cloud-free area. Hurricane Impacts
Storm surge is a large dome of water often 50 to 100 miles wide that sweeps across the coastline near where a hurricane makes landfall. The surge of high water topped by waves is devastating. The stronger the hurricane 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.
The storm tide is the combination of the storm surge and the astronomical tide. If the storm surge arrives at high tide, the water height will be even greater. For example, as a hurricane moves ashore, a 15-foot surge added to the 2-foot high tide creates a storm tide of 17 feet. This mound of water, topped by battering waves, moves ashore along an area of the coastline as much as 100 miles wide. The combination of the storm surge, battering waves and high winds is deadly and causes great property damage.
Hurricane-force winds, 74 mph or more, can destroy buildings and mobile homes. Debris, such as signs, roofing material, siding, and small items left outside, become flying missiles in hurricanes. Winds can stay above hurricane strength well inland. Hurricane Hugo (1989) battered Charlotte, North Carolina-about 175 miles inland with gusts to near 100 mph, downing trees and power lines.
Hurricanes and tropical storms also produce tornadoes. These tornadoes most often occur in thunderstorms embedded in rain bands well away from the center of the hurricane; however, they can also occur near the eyewall. Usually, tornadoes produced by tropical cyclones are relatively weak and short-lived, but still pose a threat.
All tropical cyclones can produce widespread torrential rains often in excess of 6 inches. This rain can produce deadly and destructive floods. Heavy rain can trigger landslides and mud slides, especially in mountainous regions. Flooding is the major threat from tropical cyclones to people well inland.
Between 1970 and 1999, more people have lost their lives from freshwater flooding associated with landfalling tropical cyclones than from any other weather hazard related to tropical cyclones.
Flash flooding, a rapid rise in water levels, can occur quickly due to intense rainfall. Longer term flooding on rivers and streams can persist for several days after the storm. Intense rainfall is not directly related to the winds of tropical cyclones but rather to the speed of movement and geography of the area affected. Slower moving storms produce more rainfall. Mountainous terrain enhances rainfall from a tropical cyclone. Inland flooding can be a major threat to people hundreds of miles from the coast.
The United States has a significant hurricane problem as the coastal population continues to rapidly increase. More than one in six Americans now live in a county abutting the eastern Atlantic or Gulf of Mexico coast, and this does not include those living in Puerto Rico or Hawaii. In the more popular resort areas, numbers can swell 10- to perhaps 100-fold when holiday, weekend, and vacation visitors arrive.
From Maine to Texas, our coastlines are filling with new homes, condominium towers and cities built on sand. These homes are waiting for the next storm to threaten its residents dreams. In fact, the coastal population is expected to double between 1995 and 2010. The most significant danger to coastal citizens is from the hurricane's storm surge. Historically, storm surge has caused the greatest loss of life and extreme property damage.
Over the past several years, the hurricane warning system has provided adequate time for people on the barrier islands and the immediate coastline to move inland when hurricanes threaten. However, it is becoming more difficult to evacuate people from the barrier islands and other coastal areas because roads have not kept pace with the rapid population growth. The problem is further compounded because 80 to 90 percent of the population now living in hurricane-prone areas have never experienced the core of a "major" hurricane. Many of these people have been through weaker storms.
The result is a false impression of a major hurricane's damage potential. This can lead to complacency and delayed actions resulting in injuries and loss of lives.
During the '70s, '80s and '90s, major hurricanes striking the United States were less frequent than the previous three decades. With the tremendous increase in population along the high-risk areas of our shorelines, the United States may not fare as well in the future. Some hurricane experts think the frequency of major hurricanes making landfall in the United States will increase over the next few decades.
In the final analysis, the only real defense against hurricanes is the informed readiness of your community, your family and YOU.
All Atlantic and Gulf coastal areas as well as the U.S. Pacific Islands are subject to hurricanes/typhoons or tropical storms. Although rarely struck by hurricanes, parts of the southwest United States and Pacific Coast can experience heavy rains and floods from the remnants of hurricanes spawned off Mexico. Hawaii and the U.S. territories, such as Guam, American Samoa and Puerto Rico, are also subject to hurricanes. Hurricane Iniki struck Kauai, Hawaii, on September 11, 1992, resulting in $2.5 billion in damage. During 1992, Guam was battered by five typhoons. On December 16, 1997, Guam was hit by Super Typhoon Paka, causing over $520 million in damage.
Due to the limited number of evacuation routes, barrier islands such as the Outer Banks of North Carolina and areas like the Florida Keys and New Orleans, Louisiana, are especially vulnerable to hurricanes. People living near coastal areas may be asked by local officials to evacuate well in advance of a hurricane landfall. If you are asked to leave your home, do so IMMEDIATELY!
Geostationary satellites orbiting the earth at an altitude of about 22,000 miles above the equator provide imagery day and night. This satellite imagery is a valuable tool helping to provide estimates of the location, size and intensity of a storm and its surrounding environment.
The U.S. Air Force Reserve provides most of the hurricane reconnaissance used by the National Hurricane Center. Pilots fly into the core of a hurricane to measure wind, pressure, temperature and humidity as well as to provide an accurate location of the center of the hurricane. NOAA also flies aircraft into hurricanes to aid scientists in better understanding these storms and to improve forecast capabilities.
When a hurricane gets close to the coast, it is monitored by land-based weather radars. The NWS Doppler weather radars, equipped with the latest advanced technology, add new dimensions to hurricane warning capabilities. It provides j detailed information on j hurricane wind fields and its changes. Local NWS offices are able to provide accurate short-term warnings for floods, inland high winds and any other weather hazards associated with a tropical cyclone.
The NWS National Hurricane Center and Central Pacific Hurricane Center use several different numerical computer models to aid in forecasting the path, speed and strength of hurricanes. Data from weather satellite sensors, reconnaissance aircraft and other sources are fed into these computer models. The National Hurricane Center also has a computer storm surge model. This model provides guidance on storm surge height and the extent of flooding it will cause. Stay Informed! NOAA Weather Radio
NOAA Weather Radio (NWR) is the prime alerting and critical information delivery system of the NWS. NWR broadcasts warnings, watches, forecasts and other hazard information 24 hours a day. Known as the "voice of the NWS," the NWR network has more than 590 stations, covering the 50 states, adjacent coastal waters, Puerto Rico, the U.S. Virgin Islands and U.S. Pacific territories.
Many weather radios are equipped with a special alarm tone feature that sounds an alert giving you immediate information about a life-threatening situation. Routine weather radio programming is interrupted during tropical cyclone threats to send out the special tone that activates weather radios in the listening area. The hearing and visually impaired can get these warnings b) connecting weather radios to devices such as strobe lights pagers, bed-shakers, personal computers and text printers.
The NWS encourages people to buy a weather radio equipped with the Specific Area Message Encode (SAME) feature. This feature automatically alerts you when important tropical cyclone information is issued for your area.
More information on NOAA Weather Radio can be found by contacting your local NWS office or on the Internet at: www.nws.noaa.gov/nwr.
The NWS NOAA Weather Wire Service (NWWS) provides reliable and timely warnings. NWWS has been improved and now makes limited graphic images available through a standard computer.
The Emergency Managers Weather Information Network (EMWIN) offers an economical way to receive all products available on NWWS, plus graphical forecasts and select satellite data. For details, go to iwin.nws.noaa.i!ov/emwin/index.htm.
The Interactive Weather Information Network (IWIN) is a Web site with live data similar to EM WIN. It is open to all users and contains warnings in addition to many routine NWS products. To view TWIN products, go to http://iwin.nws.noaa.eov.
All of the above information must be used to make an informed decision on your risk and what actions should be taken. Remember to listen to your local official's recommendations and to NOAA Weather Radio for the latest hurricane information.
| More hurricane information and news is just a click away. | |
|---|---|
| National Weather Service: | www.nws.noaa.gov |
| National Hurricane Center: | www.nhc.noaa.gov |
| Central Pacific Hurricane Center: | www.nws.noaa.gov/pr/hnl/cphc/pages/cphc.shtml |
| Links to local NWS Offices | |
| NWS Eastern Region: | www.erh.noaa.gov |
| NWS Southern Region: | www.srh.noaa.gov |
| NWS Pacific Region: | www.nws.noaa.gov/pr |
| Historical Information | |
| Nat'l Climatic Data Center: | www.ncdc.noaa.gov |
| Other Emergency Information Sites | |
| American Red Cross: | www.redcross.org |
| FEMA: | www.fema.gov |
| U.S. Geological Survey: | www.usgs.gov/hurricanes |