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A hurricane pours out about two hundred times more power than every power station on Earth put together. Nobody plugs it in. So where is it coming from?
A big storm throws millions of tonnes of water into the sky, drags trees over and shoves the sea onto the land. That takes an enormous amount of energy.
It has no engine. No fuel tank. Nobody fills it up.
And yet the energy is definitely real. So something must be handing it over — and you have already felt exactly what it is.
Climb out of a warm bath and stand there dripping. You get cold. Fast. Even if the room is perfectly warm.
Why? The water on your skin is evaporating — turning from liquid into invisible vapour and floating off. And turning water into vapour takes energy. Quite a lot of it.
The water doesn't have that energy. So it takes it from you. Your skin hands over the heat, the water leaves as vapour, and you stand there shivering.
Now the important half. That energy isn't gone. It's inside the vapour, being carried around, invisible.
And when that vapour turns back into liquid water — when it condenses — it has to give the energy back. All of it. Straight into whatever air is around it, as heat.
Scientists call it latent heat, and latent just means hidden. Hidden heat. It goes into the vapour when water evaporates and comes back out when the vapour turns into a cloud droplet.
Every cloud droplet that forms warms the air a tiny bit. A storm is what happens when trillions of them form at once.
If hidden heat is the fuel, then water vapour is the fuel tank. So the next question is: how much vapour can air actually carry?
The answer depends almost entirely on how warm the air is — and it does not go up gently.
Grams of water vapour that one kilogram of air can hold before it's completely full, at sea level. Tap "See the numbers" and compare 10 degrees against 30.
| Air temperature in °C | Most vapour the air can hold |
|---|---|
| 0 | 3.8 |
| 5 | 5.4 |
| 10 | 7.6 |
| 15 | 10.6 |
| 20 | 14.7 |
| 25 | 20.1 |
| 30 | 27.2 |
Look at the shape of that line. It doesn't climb like a staircase — it curves upward, steeper and steeper.
Air at 30°C can hold about 27 grams of water in every kilogram. At 10°C it manages about 7.6 grams. That's roughly three and a half times as much fuel in the warm air, for a temperature difference you'd describe as "a hot day instead of a cool one".
This is the whole reason big storms grow over warm tropical oceans and not over cold northern ones. Warm sea, warm air above it, and that air can be absolutely loaded with hidden heat.
Two identical bodies of air are pushed upward. One started over a sea at 30°C, the other over a sea at 10°C. Which has more energy available to build a storm, and why?
Weather forecasters list three ingredients for a thunderstorm, and every one of them has now turned up in this episode:
With all three, the loop below starts. And it feeds itself.
This is the engine. Press to take the next step, and watch for the moment it stops needing a push.
Six situations. Sort each one by what it does to a storm, and read why — a couple of these are the opposite of what they look like.
Tap an item, then tap where it belongs
A hurricane has been growing for days out at sea. It comes ashore and weakens quickly, even though the land below it is hot. What ran out?
For a hurricane to get going at all, the ocean underneath usually has to be around 80°F (about 27°C) — and warm all the way down to a depth of roughly 150 feet, not just a thin sun-warmed skin on top. A hurricane churns the sea as it goes, so a shallow warm layer gets stirred away and the storm cools its own fuel supply.
When the conditions are right, here is what one average hurricane does.
Making its clouds and rain releases about six hundred trillion watts of heat. That is roughly two hundred times all the electricity every power station on Earth can make.
Only a sliver of that ever becomes wind. The energy in the swirling winds themselves comes to about one and a half trillion watts — still around half of the world's entire electricity-making capacity, from one storm's wind alone.
And it is raining the whole time: an average hurricane drops about 1.5 centimetres of rain a day across a circle roughly 665 kilometres in radius.
Every drop of that used to be sea water. Every drop was lifted into the sky by the sun, carried invisibly, and then handed its hidden heat back to the storm on the way down.
A hurricane isn't really a thing. It's a process — an enormous, self-feeding transfer of heat from a warm ocean into the sky.
A hurricane's winds carry about a hundredth as much energy as its clouds and rain release. What does that tell you about a storm?
You’re previewing as a parent — nothing here is recorded.
Thunderstorms require three ingredients: moisture, instability (warm moist air near the surface with colder air aloft, so a lifted parcel keeps rising), and a lifting mechanism. As a parcel rises it cools, water vapour condenses, and the released heat builds cumulonimbus cloud. (NOAA JetStream, "Ingredients for a Thunderstorm"; NWS spotter guide; NOAA NESDIS, "What Causes a Thunderstorm?".) Latent heat of condensation is the driving energy for storm intensification: water vapour is the fuel, releasing its stored heat when it condenses and warming the surrounding air. (NOAA/AOML Hurricane Research Division; University of Arizona ATMO 336 course notes, "Latent heat of water: the fuel of hurricanes".) Chart values are saturation mixing ratios at sea-level pressure (1013.25 hPa), computed as w = 622 x es / (p - es) with the standard Magnus formula es = 6.112 x exp(17.67T / (T + 243.5)) hPa: 3.8 g/kg at 0°C, 5.4 at 5°C, 7.6 at 10°C, 10.6 at 15°C, 14.7 at 20°C, 20.1 at 25°C, 27.2 at 30°C. The 20°C and 30°C values match the standard published meteorological table. The ratio quoted in the episode, 27.2 / 7.6, is about 3.6 — described as "roughly three and a half times". Hurricane formation conditions: ocean waters around 80°F at the surface and warm to a depth of about 150 feet. (NOAA/AOML Hurricane Research Division FAQ.) Hurricane energy, from the same NOAA/AOML FAQ: heat released in cloud and rain formation, 5.2 x 10^19 Joules/day, which is 6.0 x 10^14 Watts — about 200 times the world's electrical generating capacity. Kinetic energy of the winds, 1.3 x 10^17 Joules/day, or 1.5 x 10^12 Watts — about half of world electrical generating capacity. The episode's "six hundred trillion watts" and "one and a half trillion watts" are those two figures written out. Rainfall: an average hurricane produces 1.5 cm/day (0.6 inches/day) of rain inside a circle of radius 665 km. (Same NOAA/AOML FAQ.) This episode explains the physics of a storm. It gives no weather-safety instructions, which are a grown-up's responsibility and a different document.