Hurricanes...Unleashing Nature's Fury

A PREPAREDNESS GUIDE
 
U.S. DEPARTMENT OF COMMERCE 
National Oceanic and Atmospheric Administration 
National Weather Service
 March 1994 
NOAA, FEMA, and The American Red Cross

What is a Hurricane?

Breeding Grounds

In the eastern Pacific, hurricanes start forming by mid-May. In the Atlantic, Caribbean, and Gulf of Mexico, hurricanes season starts  in June. For the United States, 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.

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.

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. For example as hurricane moves ashore, a 15-foot surge added to the normal 2-foot 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.

Storm Tide Facts

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, downing trees and power lines and causing massive disruption.

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.

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.

Who Is 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. 

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.

The US 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 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 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.

Surveillance and Forecasting

Satellite

Geostationary satellites orbiting the earth at an altitude of about 22,000 miles above the equator provide imagery both day and night. The satellite imagery helps provide estimates of the location, size, and intensity of a storm and its surrounding environment.

Reconnaissance Aircraft

The US Air Force Reserve provides most of the operational reconnaissance. Pilots fly aircraft 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. The National Oceanic and Atmospheric Administration also flies aircraft into hurricanes to aid scientists in better understanding these storms and to improve forecast capabilities. The NOAA flights also provide operational support as required.

Radar

When a hurricane gets close to the coast, it is monitored by land-based weather radars. The National Weather Service is currently installing Doppler weather radars across the country which will add new dimensions to hurricane warning capabilities. They will provide detailed information on hurricane wind fields and their changes. Local NWS offices will be able to provide more accurate short-term warnings for floods, tornadoes, and inland high winds.

National Hurricane Center Models

The National Hurricane Center uses 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.

What To Listen For....

NOAA Weather Radio is the best means to receive warnings from the National Weather Service

The National Weather Service continuously broadcasts updated hurricane advisories that can be received by NOAA Weather Radios sold in many stores. The average range is 40 miles, depending on topography. Your National Weather Service recommends purchasing a radio that has both a battery backup and a tone-alert feature which automatically alerts you when a watch or warning is issued.

Information for Local Decision Makers

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.

Personal and Community Preparedness

Individuals with special needs or others requiring more information should contact their local National Weather Service office, emergency management office, or American Red Cross chapter.

When in a Watch Area...

Plan to evacuate if you...

When in a Warning Area...

What to bring to a shelter: first-aid kit; medicine; baby food and diapers; cards, games, books; toiletries; battery-powered radio; flashlight (one per person); extra batteries; blankets or sleeping bags; identification, valuable papers (insurance), and cash.

Reminder! If you ARE told to leave, do so immediately!

If Staying in a Home...

Only stay in a home if you have NOT been ordered to leave. Stay inside a well constructed building. In structures, such as a home, examine the building and plan in advance what you will do if winds become strong. Strong winds can produce deadly missiles and structural failure.

If winds become strong...

Be Alert For:

Each community subject to a hurricane threat should develop its own hurricane safety plan. After you have developed a personal/family safety plan, you may want to find out about your community safety plan. Your local officials should have the most detailed information for your immediate area. Please listen to and follow their recommendations both before, during, and after the storm.

FAMILY DISASTER PLAN

Families should be prepared for all hazards that could affect their area. NOAA's National Weather Service, the Federal Emergency Management Agency, and the American Red Cross urge every family to develop a family disaster plan.

Where will your family be when disaster strikes? They could be anywhere at work, at school, or in the car. How will you find each other? Will you know if your children are safe? Disaster may force you to evacuate your neighborhood or confine you to your home. What would you do if basic services water, gas, electricity or telephones were cut off?

Follow these basic steps to develop a family disaster plan...

I. Gather  information about hazards. Contact your local National Weather Service office, emergency management office, and American Red Cross chapter. Find out what type of disasters could occur and how you should respond. Learn your community's warning signals and evacuation plans.

II. Meet with your family to create a plan. Discuss the information you have gathered. Pick two places to meet: a spot outside your home for an emergency, such as fire, and a place away from your neighborhood in case you can't return home. Choose an out-of-state friend as your "family check-in contact" for everyone to call if the family gets separated. Discuss what you would do if advised to evacuate.

III. Implement your plan.