Hurricanes
A hurricane is a giant heat engine powered by warm ocean water, and when it runs out of fuel it falls apart.
By Greg Goodwin · Published October 16, 2026 · Updated October 24, 2026
Cheat Sheet
- Definition: a tropical cyclone with sustained winds of at least 74 mph (119 km/h) in the Atlantic or eastern Pacific.
- Other names: typhoon in the northwest Pacific; cyclone in the Indian Ocean and South Pacific.
- Fuel: ocean water of roughly 26.5 C (80 F) or warmer, to a depth of about 50 meters.
- Season: Atlantic hurricane season runs June 1 to November 30, peaking around September 10.
- Scale: Saffir-Simpson Category 1 (74-95 mph) to Category 5 (157 mph or higher), based on wind only.
- Deadliest hazard: storm surge historically causes the most deaths, followed by inland flooding from rain.
The 60-Second Version
Hurricanes form over warm tropical oceans when moist air rises, cools, and condenses, releasing heat that drives the air higher and pulls in more air from below. Earth's rotation bends the inflowing air into a spiral, so the whole system spins, counterclockwise in the Northern Hemisphere. Thunderstorms organize into bands around a calm center called the eye, and if conditions are favorable, such as warm water and light winds aloft, the storm intensifies. Landfall cuts off its fuel supply and adds friction, so it weakens inland, but it can still unleash destructive flooding. The greatest dangers are storm surge, which drowns coastal areas, followed by flooding rain and wind. Forecasters now predict storm tracks well several days ahead, though intensity remains harder to predict.
The Long Version
How a Storm Grows
Most Atlantic hurricanes start as clusters of thunderstorms moving off the coast of Africa. If sea temperatures are high, the atmosphere is moist, and there is little wind shear, the cluster can organize into a tropical depression, then a tropical storm once winds reach 39 mph, and a hurricane at 74 mph. Hurricanes need to be at least a few degrees of latitude from the equator, where the Coriolis effect is strong enough to start rotation. Heat released as water vapor condenses supplies the energy, comparable to many times the world's electricity generation.
Inside the Storm
The eye is calm because air sinks there, while the surrounding eyewall holds the fiercest winds and heaviest rain. Spiral rainbands stretch outward for hundreds of miles. The right side of a Northern Hemisphere hurricane, relative to its motion, is usually the most dangerous because the storm's forward speed adds to its winds. Hurricanes can produce tornadoes, especially in outer bands after landfall.
Measuring Danger
The Saffir-Simpson scale categorizes hurricanes by sustained winds, helping communicate wind damage potential. But it doesn't include water. Storm surge can reach over 20 feet in major storms: the 1900 Galveston hurricane killed an estimated 8,000 people, and Hurricane Katrina's surge in 2005 devastated the Gulf Coast and contributed to roughly 1,800 deaths. Slow-moving storms like Harvey in 2017 can drop several feet of rain. Many fatalities, including from past cyclones such as Bangladesh's 1970 Bhola cyclone, come from water rather than wind.
Forecasting and Preparing
The National Hurricane Center issues forecasts, watches, and warnings. Aircraft, known as hurricane hunters, fly into storms to measure pressure and winds, and satellites, buoys, and computer models add data. Track errors have fallen substantially over decades, which saves lives by allowing earlier evacuations. Intensity forecasts, especially for rapid intensification, remain a challenge. Residents in hurricane zones should know evacuation routes, heed local officials, and have supplies ready.
A Warming World
Scientists have high confidence that climate change is raising sea levels, which worsens surge, and increasing rainfall rates in tropical cyclones. Evidence also suggests a greater share of storms reaching the strongest categories, and more cases of rapid intensification. The effect on the total number of storms is less clear. Researchers continue to study how these trends will play out.
Why People Care
Hurricanes affect millions of people and cause tens of billions of dollars in damage in a bad year. Knowing how they work helps with preparation, with interpreting forecasts, and with understanding how a changing climate may shape future risks.
Glossary
- Eye
- The calm, often clear center of a hurricane, typically 20 to 40 miles across.
- Eyewall
- The ring of intense thunderstorms around the eye, where the strongest winds occur.
- Storm surge
- Abnormal rise of seawater pushed onshore by a storm's winds.
- Rapid intensification
- An increase in maximum sustained winds of at least 35 mph within 24 hours.
- Wind shear
- A change in wind speed or direction with height, which can tear a developing storm apart.
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