Tropical cyclones

0:00- [Narrator] What starts as a warm ocean air can quickly grow into one of nature's most powerful forces, a tropical cyclone. But how does that transformation even happen? Let's find out. Tropical cyclones are intense storms that form over warm tropical or subtropical waters.

0:21They go by different names depending on where they occur, like hurricanes in the Atlantic, typhoons in the Northwest Pacific, and they just call it cyclones in the Indian Ocean and the Southwest Pacific. But it doesn't matter what their names are, they all form in the same way.

0:39It all begins with warm ocean water, at least 80 degrees Fahrenheit. Okay? That heat warms the air just above the surface. And as this warm, moist air rises, it carries water vapor into the atmosphere. And then something important happens. Condensation. As the water vapor condenses into clouds, it releases heat, and that heat warms the surrounding already rising air, making it rise even faster.

1:16Now, all this rising air leaves behind a low pressure area near the ocean's surface. And as a result, the surrounding air rushes in to fill that gap. Now, this new air picks up heat and moisture as well, and it again rises and the cycle continues, and this cycle helps the storm grow stronger over time.

1:39But there is a twist. Because of Earth's rotation, the moving air curves, making the storm spin. This is called the Coriolis Effect. We've talked about this in detail in a separate video, but in short, because Earth spins faster at the equator compared to the poles, winds in the Northern Hemisphere always deflect to the right.

2:02So as the air moves towards the low pressure center of the storm, they keep getting deflected to the right, making them spin in the counterclockwise direction. So it's the Earth's rotation that makes them spin. And look, these tropical cyclones always rotate counterclockwise in the Northern Hemisphere.

2:21And in the Southern Hemisphere, it's the exact opposite. Winds deflect to the left, making the storms rotate clockwise. And by the way, for more details, do check out our video on the Coriolis Effect. And look, the center of the storm is low pressure, an area of calm, surrounded by fierce winds and rain.

2:40This is the eye of the storm. Anyways, the storm keeps growing as long as it stays over warm water with moist air above. Over time, it strengthens and goes through four stages. The first stage is called the tropical disturbance. By the end of this stage, we have a group of thunderstorms forming over warm waters.

3:00Okay? Then comes tropical depression. By now, winds start to rotate, but they still stay below the speed of 38 miles an hour. Then comes tropical storm. The winds have strengthened and they're now spinning at a speed somewhere between 39 to 73 miles per hour. And now the storm gets a name, for example, Tropical Storm Irene.

3:27Finally, we have the full fledged tropical cyclone. The winds now have reached 74 miles an hour or more. Now the name gets upgraded. Tropical Storm Irene becomes Hurricane Irene, for example. And in the Northern Hemisphere, these hurricanes are classified using something called the Saffir-Simpson Scale.

3:47This ranks the hurricanes from Category 1, which is the least intense, to Category 5, which is the most intense. And this is based on the wind speed. And when it comes to naming, well, there are different rules for naming cyclones in different parts of the world.

4:04For example, in Atlantic, the storms are named alphabetically, like Andrea, Barry, Chantal, Dexter, Erin. You can see that there are alternating men's and women's names. But in places like say, Indian Ocean, each country submits names in turns. So we get names like Gulaab from Pakistan, or Mocha from Yemen.

4:27Okay, finally, what happens when a tropical cyclone reaches land or cooler water? Well, it begins to weaken. Why? Well, because tropical cyclones draw energy from warm, moist air, remember? Over land or cold water, well, there's just less of it. So the storm's rising air starts to slow down and sink.

4:49And the dry air and the friction that we get from land, like say from the mountains or forest, they can also break up the storm's structure. But remember, even a weakening storm can be super dangerous. I mean, heavy rains can cause flooding, and strong winds can uproot trees and even damage homes far inland.

5:09So to put it all together, tropical cyclones are powerful rotating storms with a low pressure center formed over warm ocean water. They grow through rising, moist air and condensation fueled by the heat from the ocean. The Coriolis Effect gives them their spin.

5:25And when they reach land or cooler waters, they weaken, but not before leaving a powerful impact. Understanding how these tropical cyclones form can help us prepare for and respond to some of the Earth's most extreme weather events.