Related Items Learn how meteorologists forecast and track hurricanes. What's a Category 3 Hurricane? Check out the Saffir-Simpson Scale. Believe it or not, people fly into hurricanes to learn more about them. Read a Washington Post story about one man's journey into the eye of a hurricane. A Washington Post story outlined the tasks and mission of the NOAA's hurricane chasers. Go to Hurricane Introduction Go to Hurricane Center front page. Editor's Note: The information on this page was obtained from the National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratory.

Hurricanes: An Explainer · Defining a Hurricane · Storm Structure · Breeding Grounds · Storm Fury · Areas at Risk · The United States Hurricane Problem Hurricanes. There are no other storms like hurricanes on earth. Views of hurricanes from satellites located thousands of miles above the earth show how unique these powerful, tightly coiled weather systems are. Defining a Hurricane 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: Saffir-Simpson Hurricane Scale Category Winds Damage 1 74-95 Minimal 2 96-110 Moderate 3 111-130 Extensive 4 131-155 Extreme 5 155+ Catastrophic You can get more information about the Saffir-Simpson Scale here. 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," and similar storms in the Indian Ocean are called "cyclones." Hurricanes are products of the tropical ocean and atmosphere. Powered by heat from the sea, they 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, they sweep the ocean inward while spawning tornadoes and producing torrential rains and floods. Each year on average, ten 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 3 years. Of these five, two will be major hurricanes (category 3 or greater on the Saffir-Simpson Hurricane Scale). Timely warnings have greatly diminished hurricane fatalities in the United States. In spite of this, property damage continues to mount. There is little we can do about the hurricanes themselves. However, NOAA's National Hurricane Center and National Weather Service field offices team up with other Federal, State, and local agencies; rescue and relief organizations; the private sector; and the news media in a huge warning and preparedness effort. Back to the Top Storm Structure The process by which a disturbance forms and subsequently strengthens into a hurricane depends on at least three conditions. Warm waters and moisture are mentioned above. The third condition is 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 allow for additional strengthening. The center, or eye, of a hurricane is relatively calm. The most violent activity takes place in the area immediately around the eye, called the eyewall. 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. Back to the Top Breeding Grounds In the eastern Pacific, hurricanes begin forming by mid-May, while in the Atlantic, Caribbean, and Gulf of Mexico, hurricane development starts in June. 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 Pacific, hurricanes can occur year-round. Developing hurricanes gather heat and energy through contact with warm ocean waters. The addition of moisture by evaporation from the sea surface powers them like giant heat engines. Back to the Top Storm Fury Storm Surge 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. Storm Tide If the storm surge arrives at the same time as the high tide, the water height will be even greater. The storm tide is the combination of the storm surge and the normal astronomical tide. Storm Tide Facts over 6,000 people were killed in the Galveston Hurricane of 1900-most by the storm tide. Hurricane Camille in 1969 produced a 25-foot storm tide in Mississippi. Hurricane Hugo in 1989 generated a 20-foot storm tide in South Carolina. Heavy Rains/Floods Widespread torrential rains often in excess of 6 inches can produce deadly and destructive floods. This is the major threat to areas well inland. Tropical Storm Claudette (1979) brought 45 inches of rain to an area near Alvin, Texas, contributing to more than $600 million in damage. Long after the winds of Hurricane Diane (1955) subsided, the storm brought floods to Pennsylvania, New York, and New England that contributed to nearly 200 deaths and $4.2 billion* in damage. Hurricane Agnes (1972) fused with another storm system, producing floods in the Northeast United States which contributed to 122 deaths and $6.4 billion* in damage.* Adjusted to 1990 dollars. Winds Hurricane-force winds, 74 mph or more, can destroy poorly constructed buildings and mobile homes. Debris, such as signs, roofing material, siding, and small items left outside, become flying missiles in hurricanes. Winds often stay above hurricane strength well inland. Hurricane Hugo (1989) battered Charlotte, North Carolina (which is about 175 miles inland), with gusts to near 100 mph, dawning trees and power lines and causing massive disruption. Tornadoes Hurricanes also produce tornadoes, which add to the hurricane's destructive power. 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. Back to the Top Areas at Risk Coastal Areas and Barrier Islands All Atlantic and Gulf coastal areas are subject to hurricanes or tropical storms. Although rarely struck by hurricanes, parts of the Southwest United States and Pacific Coast suffer heavy rains and floods each year from the remnants of hurricanes spawned off Mexico. Islands, such as Hawaii, Guam, American Samoa, and Puerto Rico, are also subject to hurricanes. During 1993, Guam was battered by five typhoons. Hurricane Iniki struck the island of Kauai, Hawaii, on September 11, 1992, resulting in $1.8 billion damage. Due to the limited number of evacuation routes, barrier islands are especially vulnerable to hurricanes. People on barrier islands and in vulnerable coastal areas may be asked by local officials to evacuate well in advance of a hurricane landfall. If you are asked to evacuate, do so IMMEDIATELY! Inland Areas Hurricanes affect inland areas with high winds, floods, and tornadoes. Listen carefully to local authorities to determine what threats you can expect and take the necessary precautions to protect yourself, your family, and your property. Camille - August 14-22, 1969: 27 inches of rain in Virginia caused severe flash flooding. Agnes - June 14-22, 1972: Devastating floods from North Carolina to New York produced many record-breaking river crests. The storm generated 15 tornadoes in Florida and 2 in Georgia. Hugo - September 10-22, 1989: Wind gusts reached nearly 100 mph as far inland as Charlotte, North Carolina. Hugo sustained hurricane-strength winds until shortly after it passed west of Charlotte. Andrew - August 16-28, 1992: Damage in the United States is estimated at $25 billion, making Andrew the most expensive hurricane in United States history. Wind gusts in South Florida were estimated to be at least 175 mph. Back to the Top The United States Hurricane Problem Population Growth The United States has a significant hurricane problem. Our shorelines attract large numbers of people. From Maine to Texas, our coastline is filled with new homes, condominium towers, and cities built on sand waiting for the next storm to threaten its residents and their dreams. There are now some 45 million permanent residents along the hurricane-prone coastline, and the population is still growing. The most rapid growth has been in the sunbelt from Texas through the Carolinas. Florida, where hurricanes are most frequent, leads the Nation in new residents. In addition to the permanent residents, the holiday, weekend, and vacation populations swell in some coastal areas 10- to 100-fold. A large portion of the coastal areas with high population densities are subject to the inundation from the hurricane's storm surge that historically has caused the greatest loss of life and extreme property damage. Perception of Risk Over the past several years, the warning system has provided adequate time for people on the barrier islands and the immediate coastline to move inland when hurricanes have threatened. 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 by the fact that 80 to 9O 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 hurricane's damage potential. This often leads to complacency and delayed actions which could result in the loss of many lives. Frequency of Hurricanes During the 70's and 80's, 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, we may not fare as well in the future. This will be especially true when hurricane activity inevitably returns to the frequencies experienced during the 40's through the 60's. In the final analysis, the only real defense against hurricanes is the informed readiness of your community, your family, and YOU. All hurricanes are dangerous, but some are more so than others. The way storm surge, wind, and other factors combine determines the hurricanes destructive power. To make comparisons easier and to make the predicted hazards of approaching hurricane clearer to emergency forces-National Oceanic and Atmospheric Administration's hurricane forecasters use a disaster-potential scale which assigns storms to five categories. Category 1 is a minimum hurricane; category 5 is the worst case. See the above chart for information. Back to the Top © Copyright The Washington Post Questions? Comments? Suggestions? E-mail weather@weatherpost.com.