SolveYourProblem Article Series: Hurricanes
Hurricane Facts, Tips and Safety Protocols

How Does A Hurricane Form?

Hurricane season threatens the eastern and gulf coasts of the United States, Mexico, and the Caribbean every year between June 1 and November 30. In other parts of the world, the same types of storms are generally called typhoons or cyclones. Hurricanes wreak havoc when they hit and they can kill thousands of people and cause billions of dollars in property damage when they hit heavily populated areas.

According to the National Hurricane Center, a hurricane is a tropical cyclone that occurs in the Atlantic Ocean. “Tropical cyclone” is the generic term used for low-pressure systems that develop in the tropics. Tropical cyclones with maximum sustained surface winds of less than 17 meters per second are called tropical depressions. Once the tropical cyclone reaches winds of at least 17 meters per second, they are called a tropical storm and assigned a name. If the winds reach 33 meters per second, it is then termed a hurricane.

Hurricanes are defined by the following characteristics. They are tropical, which means they are generated in tropical areas of the ocean near the Equator. They are cyclonic, which means that their winds swirl around a central eye. The wind direction is counterclockwise, or west to east, in the Northern Hemisphere. The wind direction in the Southern Hemisphere is clockwise, or east to west. Hurricanes are low-pressure systems as the eye of a hurricane is always a low-pressure area. The lowest barometric pressures ever recorded have always occurred inside hurricanes. Plus, the winds swirling around the center of the storm have a sustained speed of at least 74 miles per hour.

Hurricanes form in tropical regions where there is warm water, typically at least 80 degrees Fahrenheit and 27 degrees Celsius, moist air and converging equatorial winds. Most Atlantic hurricanes begin off the west coast of Africa and start out as thunderstorms that move out over the warm and tropical ocean waters. A thunderstorm reaches hurricane status in three stages. A tropical depression has swirling clouds and rain with wind speeds of less than 38 miles per hour. A tropical storm has wind speeds of 39 to 73 miles per hour and a hurricane has wind speeds greater than 74 miles per hour. It can take anywhere from a couple of hours to several days for a thunderstorm to develop into a hurricane. Although the entire process of hurricane formation is not entirely understood, three events must occur for a hurricane to form. A continuing evaporation and condensation cycle of warm and humid ocean air must occur. Patterns of wind characterized by converging winds at the surface and strong, uniform-speed winds at higher altitudes must also occur. Lastly, a difference in air pressure, called pressure gradient, must occur between the surface and the high altitude.

Warm and moist air from the ocean surface begins to rise rapidly. As this warm air rises, its water vapor condenses to form droplets of rain and storm clouds. The condensation releases heat known as latent heat of condensation. This latent heat warms the cool air, which causes it to rise. This rising air is replaced by more warm and humid air from the ocean below. The cycle continues, drawing more warm and moist air into the developing storm and continuously moving heat from the surface to the atmosphere.

The exchange of heat from the surface creates a pattern of wind that circulates around a center. High-pressure air in the upper atmosphere over the storm’s center also removes heat from the rising air, which further drives the air cycle and the hurricane’s growth. As high-pressure air is sucked into the low-pressure center of the storm, wind speeds increase. Once a hurricane forms, it has three main parts, which include the eye, the eye wall, and rain bands. Rain bands are bands of thunderstorms circulating outward from the eye that are part of the evaporation and condensation cycle that feeds the storm.

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by SolveYourProblem.com : 2007

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