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Hurricanes vs. Tornadoes

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On this week's Iowa's Weather Wonders, Teagan Damme from Lou Henry Elementary asked if hurricanes and tornadoes are the same.

Although tornadoes and hurricanes may share in some of the ingredients necessary for their formation, too much or too little of one ingredient could be detrimental to its livelihood. Also, tornadoes and hurricanes form in different environments. Let's start first with hurricane formation.

Hurricanes are the final product, so you have to look all the way back at what makes up these devastating storms and where they originate. Lets use the Atlantic basin as an example.

Tropical waves form over Africa. The hot and dry air from the Sahara Desert collides with cooler, humid air from the Gulf of Guinea, thus creating this wave. The sharper the contrast in temperature, the stronger the wave becomes.

As the wave propagates, showers and thunderstorms can develop along the eastern edge of the wave. Warm, moist air over equatorial waters will rise and eventually condense in the atmosphere, thus producing clouds. If this activity continues and thunderstorm development is continual, the tropical wave can become a tropical depression or cyclone. These storms have sustained wind speeds of 38 mph.

For a tropical cyclone to maintain or increase in strength, it needs warm waters, light winds, and low shear. Sea surface temperatures need to be at least 80 degrees Fahrenheit to help fuel the cyclone. Steering winds and shear are also integral for the movement and strengthening of the cyclone. Steering winds help guide the cyclone across these waters, but too strong of winds can tear the storm apart. Low vertical shear helps storms continue to develop within the cyclone. However, too strong of shear can also destroy cyclones. Depressions will form into tropical storms when sustained wind speeds reach or exceed 39 mph.

Hurricanes develop when sustained wind speeds reach at least 74 mph.

Hurricanes are ranked for their sustained wind speeds on the Saffir-Simpson scale. For a detailed explanation on the classification of hurricanes and their strength according to the scale, click here.

Now switching over to tornadoes...

The tornado formation process begins when upper-level winds become stronger than surface winds, thus creating a horizontal, rotating column of air.

As thunderstorms develop, updrafts associated with these storms will pull in the rotating column of air.

Stronger updrafts create a tighter and faster rotating column of air.

Most tornadoes form in Supercell thunderstorms. The rotating portion of these storms is called a mesocyclone. Most notably seen in a supercell is the rotating wall cloud, in which tornadoes will form.

For tornadoes to form, thunderstorm gusts cool as they reach the surface and are tilted vertically by the updraft. These two columns of air meeting can create a tornado. They can also form as winds are sucked into the mesocyclone and stretched vertically. When wind speed increases, rotation will extend downward. The first theory is supported by newer research, but the latter was first developed. Not all supercells produce tornadoes. The circulation extending from the wall cloud needs to reach all the way to the ground for it to be classified as a tornado. There's still plenty of research that's being conducted on tornado formation and scientists are coming closer to understanding all aspects of tornado formation.

Tornadoes are ranked on the Enhanced Fujita Scale, which associates observed damage to potential wind speeds of a tornado. The scale ranges from EF0-EF5, with EF5 tornadoes causing catastrophic damage to life and property. Below you get a visual representation of a tornado and how it compares to each rating on the scale.

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Joie Bettenhausen


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