Forecasting Hurricanes & Creating Advisories

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  • 0:01 Hurricanes
  • 3:47 Hurricane Forecasting
  • 6:32 Saffir-Simpson Scale
  • 7:32 Lesson Summary
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Lesson Transcript
Instructor: Linda Fye
Understand the severity of hurricanes and how they develop. Learn how scientists are able to gather data on, track, predict, and categorize hurricanes. Know how hurricane advisory systems work.


On August 23, 2005, a tropical storm named Katrina moved northwest, out of the Bahamas. It strengthened to a category one hurricane before crossing over to Florida. The storm intensified over the warm waters of the Gulf of Mexico and moved north. It continued to grow stronger for a couple of days until it became a category five hurricane, the most severe and devastating kind. Wind speeds were over 170 miles per hour. It hit the Gulf Coast on August 29th near New Orleans, Louisiana. They received over 15 inches of rain in some places and Katrina produced at least two tornados. The most devastating part of the storm, however, was the massive storm surge, or water pulled on shore by the hurricane. As much as 28 feet of water covered the city and thousands of people were trapped in the floods. Loss of life in the tragedy is unknown, but it is thought to be over 1200 people. Tens of thousands of survivors had to leave their homes.

Despite the tragedy that hurricane Katrina was, it could have been much worse if hurricane forecasting and warning systems were not as advanced as they are. In this lesson, you will learn how a hurricane develops and how scientists use this information to forecast and warn people in time to save lives.

Hurricanes are very intense, low pressure disturbances or storms that have a very strong wind speed. They develop in the middle of the ocean in the warm water tropics near the equator. The moisture and warm temperature of the water create an unstable environment that allows air to rise. The rising air creates low pressure that can develop into a large storm that we know as a hurricane. As air rises within the disturbance, it moves to a higher and cooler part of the atmosphere. When the air is cooled, condensation allows water vapor to form and this moisture causes clouds to develop and precipitation to fall. This starts a cycle that powers the storm by allowing more air to rise faster and the whole disturbance becomes more unstable. As the storm becomes more unstable, it begins to pull in more and more warm moist air. It is this process that causes a minor disturbance to become a full-blown hurricane.

But there are many things about hurricanes that make them quite different from other types of storms, starting with their size. Hurricanes can be very large. They are often 300 to 400 miles in diameter, but they can be as big as 600 miles across. That is as big as two or three states. Because they are so big and powerful, it is very important to have an accurate forecasting and warning system to save lives. Even though hurricanes are large, destructive storms, they start as a small disturbance in the ocean. Locating and tracking these small disturbances is the key to accurate forecasting.

An easterly wave, or a very weak low pressure system that forms near the equator in tropical and warm weather, is often how a hurricane begins to develop. In the northern hemisphere, most easterly waves form over Africa and move across the Atlantic Ocean. Almost all of them just die out, but a few get stronger and stronger until they become hurricanes. If conditions are just right, an easterly wave will form rotating winds. If the wind speeds become greater than 74 miles per hour, the storm can officially be called a hurricane.

Hurricane Forecasting

Because hurricanes can be deadly and destructive due to high winds, torrential rain and severe flooding, monitoring and forecasting hurricanes is essential to saving lives and protecting property. Several organizations across the world monitor hurricanes in different parts of the ocean. The National Hurricane Center (NHC) in Miami is responsible for hurricanes in the Atlantic and Eastern Pacific that affect North America. It is the job of the NHC to predict how strong and big hurricanes will become and to track the path these storms will take. The NHC uses information from satellites, ships, buoys, airplanes, and radars to track and forecast hurricanes. It is important to have as much information as possible from several sources to make the best predictions.

When the storm is in the middle of the ocean, satellites are the main source of information. But when hurricanes get closer to the coast, radars on land read wind speed and precipitation information. But this is just the way that information about hurricanes is collected. Before any predictions can be made, all of the collected information is fed into computer models that can then be used to make a forecast. It is only after the computer model results are compared with current information about the weather and environment that the NHC makes a forecast about strength, location and direction of a hurricane. Then the NHC gives a forecast to emergency personnel and the media so the public can know and take necessary precautions. The same process is repeated every few hours until the hurricane dissipates.

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