What is a Hurricane? - Definition and Formation

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  • 0:08 Hurricanes
  • 1:49 How Hurricanes Form
  • 3:15 Conditions Needed for…
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Hurricanes are powerful storms with sustained winds over 74 miles per hour. They form over warm ocean waters. Learn facts about hurricanes, including how they form, why they rotate and how they get stronger.


Timmy's science class was studying storms, and his teacher asked him to write a paper on hurricanes. Timmy did not know much about hurricanes, except that they were big storms capable of creating a lot of damage, so he decided to ask an expert. He took a trip down to the local TV station to ask the weatherman to explain just what hurricanes are and how they are formed. Let's follow along with Timmy and see what he finds out.

At the TV station, Timmy is greeted by weatherman Tom Raines, who is happy to help Timmy with his project. Mr. Raines explained that a hurricane is a tropical storm with constant winds of 74 miles per hour or greater. He then told Timmy that hurricanes can be enormous storms, stretching 600 miles across, and that they can last more than a week when they are located over warm ocean waters. Warm areas over oceans are what give hurricanes their energy. Hurricanes start in tropical waters and can be found in the Atlantic Ocean, Gulf of Mexico and the Eastern Pacific Ocean.

An interesting fact that Timmy discovered is that hurricanes are made up of powerful swirling winds that spin due to the Coriolis Force. This is a phenomena created by the rotation of the earth that causes free moving objects, such as the wind, to move to the right or left. Due to this phenomenon, we see that hurricanes rotate in a counter-clockwise direction in the Northern Hemisphere and clockwise direction in the Southern Hemisphere. Despite the spinning winds associated with a hurricane, there is an area at the center of the hurricane that has weak winds and fair weather called the eye.

How Hurricanes Form

At this point, Timmy felt like his head was starting to spin from all of the information he was learning, so Mr. Raines decided to break up the lecture by showing Timmy an experiment to demonstrate how hurricanes form.

Mr. Raines took Timmy into the kitchen at the TV station, where he had a pan of boiling water on the stove. Timmy noticed that the boiling water was creating steam, and he could see the moist air rising upward. Mr. Raines explained that hurricanes form over really warm waters where the water temperatures are more than 80 degrees Fahrenheit. Therefore, hurricanes typically get their start in the tropics.

These warm waters cause moisture to rise up into the atmosphere, just like the moisture rising from the pan of hot water. Mr. Raines then picked up a bowl filled with ice cubes and held it a few inches above the pan. This, he explained, represents the cooler atmosphere above the warm ocean. After a few moments, Timmy noticed that water droplets were forming on the bottom of the bowl of ice cubes. Mr. Raines said that was due to condensation, which is the process by which water droplets form on a cold surface when met by humid air. He explained that the same thing happens when warm, humid air from the ocean rises to meet the colder atmosphere. This gives us the clouds associated with hurricanes.

Conditions Needed for a Hurricane to Form

Timmy was really starting to understand how hurricanes form, but he wondered why hurricanes didn't happen all of the time, since tropical waters are always pretty warm. Mr. Raines mentioned that there were a few more conditions needed for a hurricane to form.

He explained that when this warm humid air rises, there is less air remaining at the ocean surface. This causes an area of low air pressure. Surrounding air flows toward this zone of low pressure from all directions. These converging winds begin to rotate due to the Coriolis Force. All of this air warms up and spirals upward, carrying more moisture into the atmosphere. As it rises, it makes more clouds and releases its heat. Winds above the storm blow the rising heat away, allowing more warm air to rise. This cycle continues, and the storm reinforces itself.

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