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posted: 6/10/2013 12:22 PM

Hurricanes and tornadoes are different, but powerful storms

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  • A tornado passes across south Oklahoma City May 20.

    A tornado passes across south Oklahoma City May 20.
    Associated Press


You wanted to know

"What is the difference between a tornado and a hurricane?" asked students in Elise Diaz's fifth-grade class at Prairie Trail School in Wadsworth.

Right on cue, Tropical Storm Andrea kicked off the 2013 hurricane season -- typically June through November -- during the first week of this month with winds up to 39 miles per hour, heavy rains and some spinoff tornadoes as it chugged up the Atlantic coast to the Carolinas.

Forecasters at NOAA, the National Atmospheric and Oceanic Administration, are predicting an active hurricane season, with as many as 20 of these ocean-born storms hitting the U.S. coast this year.

What's the difference between hurricanes and tornadoes?

"A tornado is a violently rotating column of air that occurs underneath a single severe thunderstorm," says Kevin Kloesel, director of the Oklahoma Climatological Survey and associate professor of meteorology at the University Oklahoma, home of the National Weather Center.

"A hurricane is a complex of many thunderstorms all rotating around the center eye."

This year may bring a bumper crop of hurricanes, but the numbers are down for tornadoes, Kloesel said.

"The average number of tornadoes in the U.S. by this time of year is over 800. We have only had 435 so far," he said.

Hurricanes cover much more territory than tornadoes. Hurricanes can span hundreds of miles and retain power and strength over several days. Once a storm at sea reaches wind speeds of 74 miles per hour, it's officially declared a hurricane. Huge storms of this size can be called typhoons or tropical cyclones in other parts of the world.

Kloesel described the differences between the two storms.

"Think of a tornado as a speed boat on a short lake, while the hurricane is like a large cruise ship. The cruise ship is slower, but can go a long way on a single fueling."

The aftermath of the storm -- the destruction -- follows the same analogy.

"A cruise ship crash is slower and would impact a larger area. A speed boat crashes, it's very quick and very destructive, and impacts a small area."

To be classified as a tornado, the wind column has to be in contact with both the ground and the base of a thunderstorm. Tornadoes have double the power of hurricanes, with winds sometimes reaching 200 mph.

Areas where cold air meets subtropical air can offer the right mix for a tornado to burst on the scene. The spring and summer months cook up the ominous weather conditions that ripen into these terrible twisters. Most tornadoes occur in the afternoon as the day becomes hotter.

Tornado Alley -- a slice of the Midwest that includes Texas, Iowa, Oklahoma and Kansas -- attracts storm chasers and meteorologists to record these highly dangerous funnel clouds.

The U.S. leads the world in numbers of tornadoes per year -- an average of 1,000, with Canada second at 100 per year. A few weeks ago, a real blockbuster of a tornado touched down in Moore, Okla. It tore across 17 miles in about a half-hour, killing 24 people and injuring 387, destroying homes and property valued at an estimated $2 billion.

"Each tornado is unique, as is every hurricane," Kloesel said. "They each present scientists with new challenges. Every time we think we have one aspect of them figured out, we see something unexpected."

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