What Is a Hurricane and How Do They Form?

Hurricane season lasts from June 1st to November 30th each year, but just what is a hurricane?

What Is a Hurricane?

A hurricane is a large, rotating storm that produces winds of 74 mph or higher. These destructive forces of nature form over warm ocean waters, and can strike land with catastrophic results.

When hurricanes do reach land, they can push walls of ocean water ashore. When these “storm surges” are coupled with heavy rain, it can result in massive flooding. Furthermore, winds from a hurricane can damage buildings and other structures.

Hurricanes fall under the umbrella of the more general term – tropical cyclone. Tropical cyclones are called different names based on their geographic locations. Hurricanes are tropical cyclones that form in the Atlantic Ocean and northeastern Pacific Ocean. In the northwestern Pacific Ocean, however, tropical cyclones are called “typhoons”. In the south Pacific and Indian Ocean, these storms are simply called “tropical cyclones” or “severe cyclonic storms.”

When a hurricane forms, the path and strength of the storm can be predicted by meteorologists. Hurricanes can be grouped into five different categories based on their wind speed. This ranking system is called the Saffir-Simpson Hurricane Wind Scale.

What is the Saffir-Simpson Hurricane Wind Scale?

  • Category 1: Winds 74-95 mph (119-153 km/hr)
  • Category 2: Winds 96-110 mph (154-177 km/hr)
  • Category 3: Winds 111-130 mph (178-208 km/hr)
  • Category 4: Winds 131-155 mph (209-251 km/hr)
  • Category 5: Winds 155 mph or higher (252 km/hr or higher)

What Causes a Hurricane?

Hurricanes form over warm ocean waters near the equator. As warm, moist air over the water rises, it is replaced by cooler air from the surrounding areas. This cool air is then warmed, and begins to rise as well. This continuous cycle causes large storm clouds to form.

These storm clouds will rotate with the spin of the Earth. If there is enough warm water to keep feeding them, these organized systems will continue to grow. In this initial phase, the storm can be referred to as a “tropical disturbance.” This is simply an area over warm ocean waters where rain clouds are building.

A tropical disturbance, given enough “fuel” (aka warm water), can grow into a tropical depression. This is a rotating thunderstorm with winds of 38 mph (62 km/hr) or less. Tropical depressions become “tropical storms” if the winds exceed 39 mph (63 km/hr).

If a tropical storm achieves sustained wind speeds of 74 mph (119 km/hr) or higher, it can be classified as a hurricane.

How Are Hurricanes Named?

The naming of tropical storms is controlled by the World Meteorological Organization. Prior to the early 1950s, tropical storms and hurricanes were only tracked by the order in which they occurred. The practice of naming hurricanes came into use in 1953, when it was determined that using short names made it easier to differentiate between concurrent storms.

Fun fact: Female names were used exclusively until 1978, when meteorologists in the Northern Pacific began giving storms male monikers as well. The United States quickly adopted this practice the following year in 1979.   

In the Atlantic, the list of hurricane names is recycled every six years, and old names will come into use again. Following the local alphabet, the letters Q, U, X, Y and Z are never used in the Atlantic. When a hurricane of a particularly devastating nature occurs (such as Hurricane Andrew in 1992), the hurricane name is taken out of use and retired.

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