How Do Hurricanes Form?

A hurricane is the most severe category of a tropical cyclone, which is a counter-clockwise spinning low-pressure system that includes thunderstorms. A hurricane’s winds can exceed 155 mph, carry six to 12 inches of rainfall and bring storm surges near the coast.

Hurricanes form in the warm waters near the equator. They are counter-clockwise spinning weather patterns that can travel at speeds up to 60 mph but that more commonly move at about 15-20 mph.

The three main requirements for the formation of a hurricane are:

• The surface water temperature needs to be 80+ degrees down to a depth of 150 feet
• There must be weather disturbances, such as thunderstorms, at the formation point
• The winds should be light and fairly steady in the upper regions of the atmosphere (i.e. there should be no wind sheer)

When these three things happen at sea you still have no guarantee that a hurricane will form, but these things all must be present in order for there to be a chance of formation.

The wind speed in these systems determines the actual name of the system:

• Tropical depression - If the wind speed is below 38 mph
• Tropical storm - Wind speed between 39-74 mph
• Hurricane - When the wind speeds exceed 74 mph

If the weather patterns continue favorably and the seas remain steady, the storm system can build and, once the winds reach 74 mph, the system will enter the hurricane stage.

Hurricane Terminology

Category

Hurricanes are classified in categories from 1 through 5. Their level of potential damage increases with the number. The wind speed and size of the hurricane is also indicated by the category. The structure of a hurricane begins in the center with the eye. The eye is an area of relative calm and can be between 20-40 miles wide. The winds are mild and there is very little sound.

Eye Wall

As you move out from the eye, the very first section you reach is that of the eye wall. The eye wall is a section of extremely dense thunderstorms and has the highest winds.

Spiral Bands

The final region of the storm is the spiral bands of rain. The spiral bands extend the rest of the way out to the edge of the hurricane and bring heavy thunderstorms with them.

Sea Surge

Hurricanes can grow as big as 500 miles long and 300 miles in diameter.  This entire area is extremely dangerous as it will bring high winds and flash flooding. If you happen to live close to a shoreline, you will also have additional things to worry about. When a hurricane makes landfall, it brings a sea surge with it. The surge can be as high as 17 feet. The damage will be worse if there is wave action on top of the surge.

The right side of the hurricane is the most dangerous part of the hurricane. The chances of extreme sea surge, winds and tornados are increased. Tropical storms and hurricanes bring with them flooding and can also cause drowning.  The decay of a hurricane generally comes when the moisture source is removed, which typically occurs when it makes landfall. As the storm moves across the landscape, friction with the storm will tend to break up the hurricane. The other forces such as wind sheer will also break up the storm.