A hurricane (called a typhoon or cyclone in other parts of the world) is among the most powerful weather events on Earth. Some generate as much energy in a single day as the entire world's electrical production. They can destroy cities. They're also genuinely beautiful from space — perfect spirals hundreds of kilometres wide. So how does one start from nothing?
Warm water is the fuel
Hurricanes need three things to form: warm ocean water (at least 26°C to a depth of 50 metres), warm moist air, and a process called the Coriolis effect to get the whole system spinning. They almost always form in tropical regions, typically late summer, when the ocean has had months to warm up.
Warm water heats the air above it. That warm, moist air rises rapidly, creating an area of low pressure at the surface. Surrounding air rushes in to fill the gap, picking up heat and moisture from the ocean as it does.
Think of the ocean surface as an enormous pan of water on a hob. When it heats up, steam rises. If you have a really powerful fan above the pan, that rising steam gets organised into a spinning column. The hurricane is the steam — the warm ocean is the hob, and the Coriolis effect is the fan giving the whole thing its spin.
The Coriolis effect
The Earth's rotation causes air flowing toward a low-pressure system to be deflected sideways — to the right in the Northern Hemisphere, to the left in the Southern Hemisphere. This deflection is what turns a simple inflow of air into a rotating system. In the Northern Hemisphere, hurricanes spin anticlockwise. In the Southern Hemisphere, the opposite.
The eye
As the storm intensifies, a calm region forms at its centre: the eye. Inside the eye, the sky is clear and winds are light — sometimes eerily calm. This is because the rotating winds are moving so fast around the centre that centrifugal force keeps air from spiralling all the way in. Surrounding the eye is the eyewall — the most destructive part of the storm, with the fastest winds and heaviest rainfall.
What makes them stop?
Hurricanes weaken when they move over cooler water (cutting off their fuel supply), when they travel over land (also cutting off the warm ocean moisture), or when wind shear in the upper atmosphere disrupts their structure. But a powerful hurricane over warm, open ocean can sustain itself for days or even weeks — and travel thousands of kilometres.
A hurricane is one of the most powerful weather events on Earth. In other parts of the world, they are called typhoons or cyclones. In just one day, some hurricanes make as much energy as all the world's electricity combined. They can destroy entire cities. From space, they look beautiful — perfect spirals hundreds of kilometres wide.
Warm water is the fuel
Hurricanes need three things to form. First, they need warm ocean water. The water must be at least 26°C and warm down to 50 metres deep. Second, they need warm, wet air. Third, they need something called the Coriolis effect to make everything spin. Hurricanes almost always form in hot, tropical parts of the world. They usually form in late summer, after the ocean has been warming for months.
The warm water heats the air just above it. That warm, wet air rises up very quickly. This creates a patch of low pressure at the surface, like a gap. Air from around the gap rushes in to fill it. As it does, it picks up more heat and moisture from the ocean.
Imagine a big saucepan of water heating up on the cooker. Steam rises up from the hot water. Now imagine a really powerful fan above the saucepan. The fan organises all that rising steam into a spinning column. In a hurricane, the warm ocean is the cooker, the rising steam is the warm wet air, and the Coriolis effect is the fan that makes it all spin round.
The Coriolis effect
The Earth is always spinning. This spinning makes moving air bend sideways. In the northern half of the world, the air bends to the right. In the southern half, it bends to the left. This bending turns a simple rush of air into a spinning storm. In the northern half of the world, hurricanes spin anticlockwise. In the southern half, they spin the other way.
The eye
As the storm gets stronger, something strange happens in the middle. A very calm area forms right at the centre. This is called the eye. Inside the eye, the sky is clear and the wind is gentle. It might feel peaceful, almost like the storm has stopped. This happens because the winds spinning around the centre are going so fast. They spin so fast that they stop air from getting all the way into the middle. Just outside the eye is a ring called the eyewall. This is the most dangerous part of the whole storm. The fastest winds and the heaviest rain are found here.
What makes them stop?
Hurricanes start to get weaker in a few different ways. They weaken if they move over cooler water. Cooler water is like taking the saucepan off the cooker — the fuel runs out. They also weaken when they move over land, because there is no more warm ocean to power them. Sometimes, strong winds high up in the sky can break the storm apart too. But a powerful hurricane over warm open ocean can keep going for days or even weeks. It can travel thousands of kilometres before it finally dies down.