Britta's Weather Lab: How do hurricanes form?
HOUSTON – Hurricanes can last for more than two weeks and travel thousands of miles across the world's oceans. Hurricanes often start as a group of thunderstorms off the coast of Africa and travel all the way to Houston. So how do hurricanes form? They follow a recipe!
Heat = Energy. Hurricanes feed off warm water. Warm water from the ocean evaporates, rising high above the ocean to make a cloud. As more clouds form, thunderstorms start to build. As long as there is a source of warm water, building thunderstorms can grow to become hurricanes! If a hurricane runs into cold water it loses energy and begins to fall apart. The magic temperature is 80 degrees. To provide enough energy for a hurricane, water temperatures need to be 80 degrees or warmer for at least 150 feet of water depth.
When thinking of hurricanes most people think of strong dangerous winds, but hurricanes need calm winds to strengthen their own ferocious winds. It sounds complicated but the idea is simple to understand by learning about wind shear.
Wind Shear is the change of wind speed and direction vertically in the atmosphere. Again it sounds complicated but it is an easy concept to understand.
Image a tower of donuts on a desk. Place a fan on the desk next to the donut tower. If the fan is on full power it will knock over the tower of donuts. This is strong wind shear! The fan is making a strong wind hit the top donuts in the tower compared to the bottom donut resting on the desk where the fan is not blowing air. The same idea applies to hurricanes.
Hurricanes are made of thunderstorms. Thunderstorms build vertically in the atmosphere growing taller and taller like a tower of donuts. If there is a strong wind high in the atmosphere, the thunderstorm is toppled over like the donut tower when the fan goes on. As long as wind shear is low, thunderstorms are able to build and strengthen allowing a hurricane to form, and also allowing for a tall tower of delicious donuts!
Putting It Together
A group of thunderstorms will slowly form into a hurricane when the recipe is perfect. With warm water and low wind shear, thunderstorms continue to grow and build. Warm air rises in the thunderstorm and eventually an area of low pressure forms in the center of the thunderstorms at the ocean's surface. The storms continue to grow and the winds inside the storm continue to strengthen. As long as the storm stays over warm water, does not hit land and has low wind shear, a hurricane eventually forms. When the winds inside the tropical system hit 39 mph, a tropical storm is formed and the storm is named. Tropical storms strengthen to a hurricane when the winds inside the storm hit 74 mph.
I hope this helps explain winter precipitation in Houston. Check out the Britta's Weather Lab page for more cool weather facts.
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