Como funcionam os furacões

Craig Freudenrich, Ph.D.,Marshall Brain

Every year, between June 1 and November 30 (period called hurricane season ), the hurricanes threaten the Gulf and east of the United States, Mexico, Central America and Caribbean coasts. In other parts of the world, the same types of storms are called typhoons or cyclones . Hurricanes spread destruction When They reach the earth and can kill Thousands of people, besides causing a loss of billions When They hit populated areas.

In this article, we discuss how hurricanes form and move and see the destruction and the damage They cause. Also we will examine how meteorologists track hurricanes.

Photo courtesy of, photographer Stuart Livingston destructive waves of Hurricane Opal (1995) at the State Pier in the city of Gulf Shores, Alabama

According to the National Hurricane Center of the United States, "Hurricane" is the name for 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 surface winds of less than 17 meters per second (62.7 km / h) are called tropical depressions . Reaches Once the tropical cyclone winds of 17 m / s, it is called a tropical storm and Receives the name (in English ). If winds reach 33 m / s (119 km / h), then it is called "Hurricane".

Source: Observatory of NASA


According to the National Hurricane Center of the United States, the word "hurricane" (English name for hurricane, inherited from the Spanish "huracán") comes from "Hurican" the Caribbean god of evil

Hurricanes are defined by the Following characteristics:

  • They are tropical , Which means They are generated in tropical areas of the ocean near the equator;
  • are cyclonic , meaning that winds are swirling around its an eye center. The wind direction is counterclockwise (west to east) in the northern hemisphere and clockwise (east to west) in the southern hemisphere;
  • They are low pressure systems . The eye of the hurricane is always an area of low pressure. The lowest barometric pressure ever recorded occurred in the interior of hurricanes;
  • winds whirl around the center of the storm with a speed of at least 119 km / h.

How is a hurricane
Hurricanes form in tropical regions where there is warm water (at least 27 ° C), atmospheric moisture and converging equatorial winds. Most Atlantic hurricane begins along the western coast of Africa, starting the violent storms that moves over the warm waters of the tropical ocean. The storm Reaches hurricane status in three stages:

  • Tropical Depression : clouds and rain with winds below 61 km / h speed swirling.
  • Tropical storm : wind speed 55-118 km / h.
  • Hurricane : wind speed over 119 km / h.

Photo courtesy NOAA Hurricane Ivan on the Gulf Coast near the United States at 14h45 (local Eastern Time) on September 15, 2004

It may take a few hours to several days for an intense storm pass the hurricane. Although the process of formation of tornado not entirely Understood, It Is Necessary Occur that three events for hurricanes to form:

  • extended-cycle evaporation condensation of warm, moist ocean air;
  • wind patterns Characterized by converging winds at the surface and strong winds and uniform speed at higher altitudes;
  • the difference in air pressure ( pressure gradient ) between the surface and altitude.

The warm and humid air from the ocean surface begins to rise rapidly. The warm air rises this, its water vapor condenses to form storm clouds and raindrops. The condensation releases heat called latent heat of condensation . This latent heat heats the cold air at high, causing it to rise. This rising air is Replaced by more warm, moist air from the ocean below. This cycle continues, dragging more warm, moist air into the storm that develops and continuously moving heat from the surface to the atmosphere. This heat transfer from the surface of the wind Creates a pattern that circulates around the center. This circulation is similar to that of water seeping by the drain.

Photo courtesy NASA composition of three views of Hurricane Andrew on days 23, 24 and August 25, 1992, the South Florida They crossed from east to west

Converging winds are winds that move in different directions. The converging winds at the surface collide and push the hot and humid air up. This rising air intensifies the air that is already rising from the surface, so that the circulation and wind speeds of the storm increases. Meanwhile, the strong winds that blow in uniform speeds at higher altitudes (up to 9000 meters) help remove the hot air rising from the storm, Which holds the continuous movement of hot air from the surface center and the storm Maintains structured. If the winds of high altitude does not blow at the same speed at all levels (if any wind shear ), the storm will lose its structure and weaken.

The high-pressure air in the upper atmosphere (above 9000 meters) above the center of the storm Also removes heat from rising air, further Top Top intensifying the air cycle and the growth of the hurricane. As the high pressure air is sucked into the low pressure center of the storm wind speed increases.

Parts of a Hurricane
Once the hurricane forms, it has three main parts:

  • Eye : the center of low pressure and calm circulation.
  • Eyewall : area around the eye with the most rapid and violent winds.
  • Streaks of rain : streaks of violent storms moving out of the eye and are part of the evaporation / condensation cycle that feeds the storm.

Source: Observatory of NASA

To know the anatomy and birth of a hurricane, see Hurricane Creation - creating a hurricane (in English). In addition, you can create a hurricane (in English) and experiment with the various factors that Affect the formation of a hurricane.


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