Tropical cyclones | How do hurricanes form?

Hurricanes are the most forceful storms on Earth. They are, without a doubt, one of the most spectacular and destructive weather phenomena. Also known as cyclones and typhoons, hurricanes are nothing more than storms that originate in the oceans, usually in late summer.

How tropical cyclones form?
How tropical cyclones form?

Where do hurricanes originate from?

For a hurricane to develop, at least three factors must come together: the temperature of the water must be higher than 26°C, so that evaporation and condensation can take place in upper layers; evaporation must generate a low pressure centre and trade winds (permanent east-to-west prevailing winds) must provide cold air in the upper layers of the atmosphere.

Because hurricanes need some specific factors to form, they can only arise in certain areas of the world. Hurricanes usually form in tropical waters north or south of the equator, where the waters are warm. In the Atlantic hurricane basin, these storms often begin with a disturbance off the west coast of Africa. Also known as the North Atlantic basin, this region includes the North Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico.

When do hurricanes occur?

There are different seasons for Atlantic and Pacific hurricanes. The Atlantic hurricane season runs from June 1 to November 30. The peak of the hurricane season usually occurs in September. The hurricane season in the eastern Pacific begins on May 15 and ends on November 30.

How do hurricanes form?

Hurricanes are meteorological phenomena that absorb heat from tropical waters as their energy source. Essentially, water vapor fuels hurricane's immense force. These storms are called by other names, such as typhoons or cyclones, depending on where they originate, but the scientific term for all these storms is tropical cyclone. 

Storm classification is based on its strength and origin location. When maximum sustained wind speed within a storm reaches 119 kms/h, it is classified as a hurricane typhoon, or tropical cyclone, depending upon where the storm originates. Only tropical cyclones that form over the Atlantic Ocean or the eastern Pacific Ocean are called "hurricanes".

When the winds in the spinning storm reach 62 km/h, the storm is called a "tropical storm". And when the wind speed reaches 119 km/h, the storm is officially a "tropical cyclone" or hurricane.

According to the U.S. National Oceanic and Atmospheric Administration, NOAA, tropical cyclones form over the ocean in an area of low pressure that moves through the humid tropics. As this climate system moves westward through the tropics, warm ocean air rises toward the storm, forming a low-pressure area just below. This causes more air to rise and cool, forming clouds and thunderstorms.

As the storm system rotates faster and faster, an eye forms in its center. Interestingly, the eye of the hurricane is a very calm and clear place with very low air pressure. High pressure air from above flows into the eye.

Hurricanes: the most forceful storms on Earth

While a hurricane occurs, strong winds can produce about half as much energy as the world's electricity generating capacity, while cloud formation and rain from the same storm could release 400 times that amount.

Tropical cyclones generally weaken when they touch land, because they are no longer fueled by the energy of the warm ocean waters. However, they tend to move inland, causing significant rain and wind damage before completely clearing up.

Hurricanes are very strong and destructive, and leave massive devastation in their wake, so when a hurricane arrives, it is ideal to be far from where the storm is headed. If you're in an area where hurricanes are common, it might be a good idea to cover all the windows in the house. 

If an evacuation is ordered, it's better to follow suit. If you do not have shelter and there is no evacuation order, it is recommended that you go into a closet or a small room without windows and stay away from glass-enclosed structures, advises NOAA.

The most devastating hurricanes in the last decade

2017 Hurricane Irma is the first major hurricane to develop in the eastern Atlantic since Hurricane Julia in 2010. Irma developed on August 30 near the Cape Verde Islands from a tropical wave, intensifying rapidly after its formation. On September 4, it became a category 5 hurricane with winds that have reached 300 kilometers per hour (sustained winds). The hurricane affected areas such as: Bahamas, Cuba, Haiti, Puerto Rico and Dominican Republic.

With $71.4 billion in damage, 2012 Hurricane Sandy was the second most costly hurricane in U.S. history after Katrina. The category 3 storm hit New York City, flooding the city's transportation systems and leaving thousands of homes destroyed. As a hurricane, it affected Cuba, Bahamas, Bermuda and Jamaica, and the United States (24 out of 50 states) and Canada. Its winds peaked at 185 km/h.

2011 Hurricane Irene made landfall in Puerto Rico, reaching North Carolina in the U.S. as a Category 1 storm. Along its course it acquired Category 3, even passing through New York City, Massachusetts or Connecticut, causing flooding, and more than $7.3 billion in overall damage. Its winds peaked at 195 km/hour.

2008 Hurricane Ike became the most costly storm in U.S. history in September 2008 with $29.5 billion in damage. This category 4 hurricane, with wind crests of up to 230 km/h, was the worst of 08' Atlantic hurricane season. Areas such as Haiti, Hispaniola, Cuba, Florida Keys, Dominican Republic, Texas or Louisiana were affected.

2007 Hurricane Felix reached category 5 on the Saffir-Simpson scale. This devastating hurricane, which took place from 21 August to 5 September 2007, wiped out more than 20,000 homes in Nicaragua. The affected areas were: Barbados, Saint Vincent and the Grenadines, Grenada, Trinidad and Tobago, Aruba, Bonaire, CuraƧao, Venezuela, Nicaragua, Honduras and El Salvador. Damage amounted to some 52 million dollars. Its winds reached gusts of up to 280 km/h.

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