How destructive are hurricanes

Hurricanes - the emergence of a force of nature

Hurricane "Laura" had reached the state of Louisiana with full force. Meteorologists warned of massive destruction from meter-high waves and destructive winds deep inland.

However, "Laura" was only the first very strong hurricane of the season. Above the unusually warm sea water, "Laura" had quickly gained strength and was upgraded from category two to category four within a few hours.

The US climate agency NOAA predicts that 2020 could be a record year for hurricanes. 19 to 25 storms are expected, of which seven to eleven could become hurricanes, three to six even very strong with wind speeds of 178 kilometers per hour and more.

Last purchases: Because of the fear of Corona, large shelters are probably unused

On average, there are twelve storms on the US Atlantic coast, three of which develop into category three, four or five hurricanes. The cyclone season ends in late November.

Recipe for a cyclone

Typhoon, hurricane and cyclone - these are three names for the same extreme weather: the tropical cyclone. It is called a typhoon off East and Southeast Asia, a cyclone off India and Australia, and a hurricane off the coast of North America. Despite different names, hurricanes occur in the same way when water of at least 26 ° Celsius evaporates over the sea.

This is also what distinguishes them from tornadoes. These non-tropical cyclones can develop anywhere there is a thunderstorm. As a result of local temperature differences, warm air strives upwards, cold air falls down, and a column of warm air screws upwards faster and faster. Tornadoes are usually only a maximum of one kilometer in diameter.

Quite different from tropical cyclones: "Hurricanes need a few basic requirements in order to be able to arise," says Andreas Friedrich, meteorologist and tornado officer at the German Weather Service (DWD). On the one hand, there is a surface temperature of the sea of ​​at least 26 degrees Celsius. The area with the warm sea water must also be sufficient, i.e. several 100 square kilometers.

A low pressure area is also missing as a further important prerequisite. "Small areas of low pressure often move from the west coast of Africa with the monsoon currents across the Atlantic into these warm waters," says Friedrich. In addition, in the development phase of the hurricane there should not be any large wind differences close to the sea and at greater heights. They would drive the storm apart.

Destructive mixture

If everything comes together, a hurricane can develop from a low pressure area. The warm, humid sea air rises, condenses in the colder heights and forms thunderclouds. The rapidly rising air creates a negative pressure on the sea surface, so that more moist air is sucked in from the environment. The air masses are drawn upwards like in a chimney. Wind speeds of up to 350 kilometers per hour arise.

The Coriolis force, which is related to the rotation of the earth, sets the air masses in rotation. "In the middle of this vortex, the 'eye' typical of a hurricane arises, in which it is very calm and cloudless, while the clouds at the edge of the eye pile up higher and higher," says Friedrich.

The slower, the more devastating

The longer these favorable cyclone conditions last, the more destructive this force of nature becomes. "The cyclones move with the help of air currents at heights of five to eight kilometers. They determine where the cyclone moves," explains Friedrich.

The storms are usually followed by floods - as here in 2019 after Hurricane Dorian

When the cyclone hits a coast, it usually loses its power quickly: the air currents of the higher atmosphere quickly drive the storm inland, cutting it off from its main source of energy - the warm, humid sea air. There they are weakened to form low pressure areas and lose their destructive power.

However, if a tropical cyclone moves very slowly and continues to be fed with moist sea air near the coast, the masses of water carried along can cause severe damage.

Stronger hurricanes thanks to climate change

Climate change ensures higher sea surface temperatures overall and thus even better conditions for hurricanes. "The larger the sea areas with a temperature above 26 degrees, the larger the areas in which hurricanes can form," says Friedrich.

Climate models suggest that there will not only be more but also stronger cyclones in the future, according to the meteorologist.

  • Cyclones - Forces of Desolation

    Typhoon and corona pandemic

    On May 14, Typhoon Vongfong devastated the city of San Policarpo in the eastern Samar Province of the Philippines with destructive winds and heavy rains. At least five people died and more than 91,000 people had to leave their homes. The Philippines are hit by numerous typhoons every year. The corona crisis exacerbates the situation even more.

  • Cyclones - Forces of Desolation

    The calm before the storm

    Another disaster has already brewed over the sea: Cyclone Amphan is heading for Bangladesh and India. Millions of people are to be brought to safety from the affected areas. In Bangladesh, the authorities fear that Amphan will be the worst cyclone since Sidr 2007 - around 3,500 people died at the time.

  • Cyclones - Forces of Desolation

    Three names - one phenomenon

    Typhoon, hurricane and cyclone - three terms for the same extreme weather: the tropical cyclone. It is called typhoon off East and Southeast Asia, hurricane off the coast of North America, and cyclone off India and Australia. Despite different names, it is created in the same way.

  • Cyclones - Forces of Desolation

    A hurricane arises

    Tropical storms occur over the sea when water at a temperature of at least 26 ° Celsius evaporates. The water vapor condenses, the air heats up and pulls cooler air up with it. Wind speeds of up to 350 kilometers per hour arise.

  • Cyclones - Forces of Desolation

    The eye of the storm

    As the earth rotates, the airflow begins to revolve around the eye of the storm, which is up to 50 kilometers in size. Here it is almost completely cloudless and calm.

  • Cyclones - Forces of Desolation

    Cyclone hits the mainland

    If the cyclone hits a coast, it will run out of propulsion because there is no more warm water to follow. The most severe damage is often caused by the masses of water that the storm brings with it from the sea. Here Vongfong meets the coastal city of Catbalogan in the particularly battered eastern part of the Philippines.

  • Cyclones - Forces of Desolation

    Announced chaos

    Sandy hit the US east coast in 2012. In terms of area, it was one of the largest cyclones that have ever been measured over the Atlantic. Tidal waves four meters high, fires, power outages, broken levees - Sandy raged over North America at more than 145 kilometers per hour. Particularly affected: New Jersey and New York.

  • Cyclones - Forces of Desolation

    Disastrous consequences

    But worse was Hurricane Katrina, which devastated New Orleans in 2005. Dams broke. Large stretches of land sank in the water. The helpers were completely overwhelmed by the forces of nature. About 1800 people died. Ten years after the disaster in the same place: some houses have been rebuilt. But many of those affected never returned.

  • Cyclones - Forces of Desolation

    Destructive vortex

    Tornadoes, on the other hand, are non-tropical cyclones. They can develop anywhere there is a thunderstorm. As a result of local temperature differences, warm air strives upwards, cold air falls down, and a column of warm air screws upwards faster and faster. Tornadoes are usually only a maximum of one kilometer in diameter.

  • Cyclones - Forces of Desolation

    Speed ​​master among storms

    The warm air, which rises quickly upwards, creates a trunk - very characteristic of a tornado. The air speeds there are enormous: the air can reach speeds of up to 500 km / h. This makes the tornado the speed world champion among cyclones.

  • Cyclones - Forces of Desolation

    Road of Desolation

    A tornado leaves a trail of destruction several kilometers long. In the American Midwest, tornadoes occur up to a few hundred times a year: There, dry and cold air from the north meets moist and warm air from the Gulf of Mexico. In Germany, tornadoes mostly rage on the coasts.

    Author: Brigitte Osterath, Clara Walther