Every year, powerful swirling storms form over tropical seas: these are hurricanes. They can devastate entire regions with their violent winds and torrential rains. But how can a hurricane emerge... from simple clouds above warm water?
Hurricane Florence seen from the International Space Station in 2018. The eye, the eyewall, and surrounding rainbands are characteristic features of tropical cyclones.
Image Wikimedia It all starts with very warm water
Hurricanes form over tropical oceans when surface water exceeds 26-27°C (79-81°F). This heat causes seawater to evaporate, creating large amounts of water vapor.
This vapor rises into the atmosphere, cools, and condenses to form clouds. As it condenses, it releases energy (known as latent heat), further warming the surrounding air. The warm air rises, drawing in cooler air from below... which sets the entire system spinning.
A natural machine that loops endlessly
Gradually, this rising column of warm air organizes itself: the system begins to rotate due to Earth's spin, an effect called the "Coriolis force." Air is drawn toward the center, where pressure is very low. Winds start rotating faster and faster around this center, known as the eye of the storm.
As long as the hurricane remains over warm ocean waters, it feeds on heat and moisture. It can grow and become extremely powerful, with winds reaching several hundred km/h (over 150 mph).
When the hurricane hits land...
Once a hurricane reaches the coast, it quickly loses strength. Why? Because it no longer has warm water beneath it to sustain it. However, its accumulated energy still causes massive damage, with flooding, violent winds, and enormous waves (called "storm surges").
With ocean warming, hurricanes are becoming more intense and wetter, even if they aren't necessarily more frequent. Scientists are closely monitoring their evolution to better predict future risks.