Not every storm that occurs in the Atlantic becomes a hurricane. Nevertheless, there are always storms of the highest category - the latest, Irma, is one of them. But what does that mean?
Image: Reuters/NOAA
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It's hurricane season in the Atlantic. From June 1 to November 30, there is a higher incidence of powerful storms. The latest is category 5 Irma, which hit several Caribbean islands on Wednesday, laying waste to homes, communities and claiming lives. It is now heading toward Florida.
With wind speeds of 250 kilometers per hour (185 miles per hour) and up, Irma is one of the most violent storms since records began. Its predecessor Harvey, which recently smashed into the US state of Texas, causing an estimated 150 to 180 billion dollars in damage, was category 4.
Strong, stronger, strongest
Irma thrashed Puerto Rico and several other Caribbean islandsImage: Reuters/A. Baez
Irma's Category 5 classification is the highest the United States' National Hurricane Center issues, and implies "catastrophic consequences." In concrete terms, the authority says that means "a large number of houses will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months."
The institution is also responsible for christening the storms. Altogether, there are six alphabetical lists, with a total of 21 male and female names each. Every year, one of the lists is chosen as the hurricanes' name-giver. After six years, the cycle starts over.
No end in sight?
Currently, about half this year's list has been used. Irma's successor, José is already on the horizon, and will be followed by Katia, which is brewing in the Gulf of Mexico.
Harvey inundated the Houston area with record rainfallImage: Reuters/Handout 2nd Lt. Faith Brodkorb/U.S. Air Force
Not all tropical storms develop into hurricanes - but José and Katia did intensify into hurricanes as of Wednesday. It's an unusually active hurricane season - and notably, one with particularly intensive storms.
This year is the first time three hurricanes are active in the Atlantic since 2010. In 1998, Hurricanes Georges, Ivan, Jeanne and Karl intensified simultaneously. The last time before that when four hurricanes were active at the same time was in August of 1893.
In the 1980s, there were only three category 5 storms, with another two the following year. From 2000 to 2010, that number rose to eight, including the most dramatic one so far: Katrina. It swept over New Orleans in 2005, and was responsible for the death of some 1,800 people. It is still regarded as the most expensive natural disaster in the history of the US.
Cyclones, typhoons, hurricanes - the power of devastation
Cyclones, typhoons and hurricanes pack a devastating punch: wherever they go, they leave a trail of destruction. But how do these powerful tropical storms arise?
Image: AFP/D. Sarkar
Social distancing impossible during Cyclone Amphan
Residents along Bangladesh's coast are being moved to safety as one of the strongest cyclones in years strikes the region. Millions of people had to be evacuated from low-lying regions along the Bay of Bengal on May 19. But plans are complicated by the coronavirus precautions. Maintaining social distancing is nearly impossible.
Image: AFP/District Administration of Bhola
Typhoon season amid the COVID-19 pandemic
On May 14, Typhoon Vongfong slammed the Philippines with strong winds and heavy rains, destroying the city of San Policarpo in the eastern province of Samar. At least five people died and more than 91,000 people were forced to leave their homes. Typhoons are not unusual in the Philippines at this time of year. But the COVID-19 outbreak lockdown measures are exacerbating the situation.
Image: AFP/A. Beronio
Three names - one phenomenon
Hurricane, typhoon, and cyclone are actually three names for the same phenomenon. Along the North American coast they are called hurricanes, in East and Southeast Asia they are called typhoons, and near India and Australia they are called cyclones. But despite the different names, they develop in the same way.
Image: Reuters
A cyclone is created
Tropical storms develop over oceans when the water temperature is at least 26 degrees Celsius (79 degrees Fahrenheit). As the warm water evaporates and condenses, the air around it heats up and drags cooler air upwards, creating powerful winds.
The eye of the storm
The Earth's rotation causes the air stream to move around the eye of the storm, which can be up to 50 kilometers wide. This area is nearly completely free of clouds and wind.
Image: picture-alliance/dpa
A storm hits land
When a tropical storm hits a coastline, it becomes weaker due to the lack of warm water. In Australia, "Marcia" was soon downgraded to a category one storm, while "Lam" weakened after striking near Brisbane. Masses of water from the sea often cause the worst damage - as seen here in China after Typhoon Nanmadol in August 2011.
Image: picture-alliance/dpa
Chaos ensues
Hurricane Sandy was one of the strongest hurricanes ever recorded over the Atlantic Ocean. It caused waves of up to 4 meters high, fires, power outages and broken dykes. Sandy arrived with winds at speeds of more than 145 kilometers per hour. Cuba, New York and New Jersey were particularly affected.
Image: Reuters
Destructive vortex
Tornadoes however, are non-tropical whirlwinds that can occur anywhere a storm is brewing. Local temperature differences force warm air upwards and cold air down, and a column of warm air rotates upwards at an increasing velocity. Tornadoes are usually only a maximum of 1 kilometer in diameter.
Fastest storms
As the warm air rises, it forms a funnel, the main characteristic of a tornado. Inside the funnel, the speed of the air can be tremendous - up to 500 kilometers per hour. Tornadoes are the fastest whirlwind type of weather phenomenon.
Image: Fotolia/Daniel Loretto
Trail of destruction
A tornado can leave a trail of destruction several kilometers long. In the US Midwest, tornadoes occur several hundred times a year, as dry, cold air from the north hits damp, warm air from the Gulf of Mexico. It's different in other countries - in Germany, for example, tornadoes occasionally occur along the coast.
