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WEATHER: What forces affect our weather?
Powerful Storms

National Hurricane Center
The Tropical Prediction Center has the latest tropical storm forecasts, as well as historical data, satellite imagery, and storm facts.

Storm Spotter's Guide
The National Oceanic and Atmospheric Administration's illustrated guide to severe storms includes photos and diagrams, a glossary, and rules for safe stormchasing. You can find the advanced guide here.

NOVA Online: Stormchasers
"A Day in the Life of a Stormchaser" features events in the life of one tornado chaser. A "Weather Facts and Events" page provides background on monsoons, hurricanes, tornadoes, and lightning, and the weather events associated with these severe storms.

Eye of the Storm: Inside a Hurricane

In the fall of 1998, Hurricane Mitch ripped through Central America, killing more than 11,000 people and leaving millions of others homeless. In Nicaragua, mudslides buried whole villages, and in Honduras, raging flood waters swept away bridges and devastated crops. "We have before us a panorama of death, desolation and ruin," said Honduras's president, Carlos Flores Facusse. "There are corpses everywhere."

Mitch was the deadliest Atlantic hurricane in the last 200 years. It was rated a Category 5 disaster on the Saffir-Simpson Hurricane Scale. In only 10 days, it caused an estimated $5 billion in damages. The death toll was higher than any hurricane since the Great Hurricane of 1780, in which 22,000 people lost their lives.

Disaster in the making: The birth of a hurricane

From June through November, it's hurricane season in the Atlantic. Hurricanes are born from tropical ocean waters. Energy from these warm waters is converted into thunderstorms. As these thunderstorms gather together, they can begin to rotate in the same direction, forming a spiral with an eye in its center. This early swirl-shaped system is called a tropical depression. As a tropical depression begins to spin and gain power, it can become a hurricane.

Not all tropical depressions become hurricanes, though. Those with wind speeds of 39-74 miles per hour are categorized as tropical storms. When a storm's wind speeds reach 74 miles per hour and greater, it is categorized as a hurricane.

A hurricane's destructive potential

Damage from hurricanes and tropical storms is usually the result of strong winds, storm surges, or heavy rain. Winds of over 100 miles per hour can tear roofs off of houses or knock trees down. Heavy rain can ruin crops, damage buildings, cause flash flooding, and spark deadly landslides such as those that occurred in Nicaragua and Honduras in 1998. During Hurricane Mitch, torrential rains of up to two feet per day were reported.

Hurricanes and tropical storms are ranked on a damage scale called the Saffir-Simpson Hurricane Scale, which takes into account their wind speed and pressure. While a Category 1 hurricane has wind speeds of 75-95 miles per hour, a Category 5 hurricane like Mitch has wind speeds of over 155 miles per hour.

Both hurricanes and tropical storms are named when they are categorized. Each year, world meteorologists come up with an alphabetical list of names that can be used for hurricanes and tropical storms that year. There is one name for each letter, except for Q, U, X, Y, and Z. In 1998, the first storm to hit was named Alex, the second Bonnie, the third Charley, and so on.

While hurricanes batter the Americas, similar storms are found in other parts of the world. In the Pacific and Indian Oceans and the China Sea, typhoons wreak havoc in coastal areas and on islands that are in the storm's path. On average, these storms are much more destructive than hurricanes. They are also three times more frequent, since they can travel for much longer over warm Pacific waters than they can over the cold waters of the Atlantic Ocean. Because these large storms affect major land areas and their populations, monitoring and predicting these storms is crucial to minimizing their harmful effects.

According to atmospheric sciences professor William Gray, 1999 could be a banner year for intense storms. Gray predicts that more than 25 storms will occur in 1999 in the Atlantic Ocean and Gulf of Mexico, at least four of which are likely to be intense hurricanes capable of causing great damage. Though the growth and progress of hurricanes can be followed very closely, their potential for devastation is great. Even with the benefit of forewarning, they are a serious weather threat.

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 "Weather" is inspired by programs from Planet Earth.


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