Like any drizzle, a hurricane forms from the evaporation of water into the atmosphere.
Obviously, the hurricane is not just any rain: it is a megastorm, with storms that can last a week and winds that exceed 200 km/h. Water evaporation also occurs in large proportions, over an area of hundreds of kilometers, and under special conditions: in the middle of the oceans, in regions of very warm waters and calm winds. Therefore, hurricanes are typically tropical phenomena.
In Brazil, scientists thought it was impossible for a hurricane to occur — the waters of the South Atlantic have a temperature lower than the 27ºC needed to generate the phenomenon. But many researchers changed their minds when the Catarina storm hit the south of the country, in 2004. “At that time, the water temperature was above normal, allowing the formation of the first Brazilian hurricane. And the structure of Catarina was identical to that of a hurricane”, says meteorologist Augusto José Pereira Filho, from the University of São Paulo (USP).
It is also worth clarifying a common question: what is the difference between hurricane, cyclone, typhoon and tornado? Hurricane, cyclone and typhoon are different names for the same phenomenon: in India and Australia, ocean storms are called cyclones. In Japan and Indonesia, typhoons. And in America, the most common name is hurricane. Tornadoes are something else. They form on the continent and are much smaller — they are between 100 and 600 meters in diameter —, last a few minutes and are much more destructive: their winds can exceed 500 km/h.
Gone with the Wind…
HURRICANE FORMATION
1. Hurricanes are born in the middle of the oceans, in places with little wind and warm waters, above 27°C. In these areas, evaporation is intense: sea water heats up, turns to steam and forms large clouds. It’s the beginning of the phenomenon
2. In the place where water evaporates, the air pressure is lower than in the surroundings. This causes air to move from areas where pressure is highest towards the center of the hurricane. This air comes full of moisture, which evaporates and makes the hurricane grow.
HURRICANE GROWTH
3. In one or two days the “bichão” is already gigantic, with 500 km in diameter and more or less 15 km in height. Throughout the area of the hurricane, it is raining and windy. Gusts vary between 118 km/h and 249 km/h
4. As a huge atmospheric phenomenon, the hurricane suffers the effects of the Earth’s rotation. It makes the air in the high pressure areas — like the top — rotate in one direction, while the air at the bottom — where the pressure is low — rotates in the opposite direction.
HIGH OF THE HURRICANE
5. In the middle of the storm is the so-called eye of the hurricane, 20 km in diameter. In this area it is very hot, there are no clouds and it does not rain. It is through this region that water continues to evaporate, fueling the hurricane
6. In the ocean, hurricanes advance in regions of warm water. Upon reaching the mainland – which is colder and drier than the sea – they lose strength and dissipate. But they cause floods, waves of up to 15 meters and strong winds.