A tornado begins as a thunderstorm, and three basic ingredients are needed for a thunderstorm, of which moisture and rising unstable air are two. A supercell is a long-lived, organized thunderstorm with a tilted, rotating updraft, a rising current of air that can be up to 10 miles wide and 50,000 feet tall and can be there 20 to 60 minutes before a tornado forms. Rising air in the storm tilts rotating air from horizontal to vertical, and once the updraft rotates and is fed by warm, moist air at ground level, a tornado can form. Tornado formation is believed to depend mainly on things that happen on the scale of the storm, in and around the mesocyclone. As of November 2026, scientists do not know exactly how a tornado funnel forms; one idea links it to temperature differences across the edge of the downdraft air.

A hurricane is built on a different bargain with the ocean. Warm ocean water feeds it: water evaporates into vapor and rises, and the warmed air is pulled into the column of clouds. Water vapor that cools and condenses back into liquid water releases latent heat, the heat that powers a hurricane. Hurricanes need water of approximately 80 degrees Fahrenheit (27 degrees Celsius) or more. The spin itself comes from the planet: Earth's Coriolis effect comes from different parts of the Earth moving at different speeds, and a hurricane, as a low-pressure system, pulls air toward its center while that effect bends the moving air. This bending of the air, the Coriolis deflection, is what makes tropical cyclones spin, counterclockwise north of the Equator and clockwise south of it. The two storms do meet, because tornadoes can be spawned by hurricanes.

Forecasting a hurricane is a matter of judgment as well as arithmetic. National Hurricane Center forecasters analyze many computer models, because no one model is right every time, and use their experience to judge which to trust. As of November 2026, the record shows that from 1991 to approximately 2015, deterministic computer models were of no use for forecasting rapid intensification, because they missed too many cases or gave false alarms. As of November 2026, predicting rapid intensification, when a hurricane quickly gets stronger, is a challenging problem for forecasters. They can also read the eye for clues: it is usually clear during rapid strengthening, and cloudy eyes are often a sign a storm is past its peak. The eye of a hurricane is a relatively calm area, typically 20 to 40 miles across, and the eyewall is a dense wall of thunderstorms surrounding it. Changes in the structure of the eyewall can change the wind speed. The spiral rainbands of a hurricane typically range from 50 to 300 miles long, and the more curved they are, the more intense the storm tends to be.

Hurricane hunting is a story of aircraft. The history of hurricane hunting starts in 1943, when Colonel Joe Duckworth of the Army Air Forces flew a single-engine trainer plane through a hurricane for the first time and showed it could be done. After that flight, interest in flying into storms grew: the Army Air Force became the Air Force, and the Air Force took over the military side of hurricane flying. Hurricane hunter missions fly to locate the center of the storm and measure its central pressure and surface winds, and dropsondes dropped from the aircraft continuously send back pressure, humidity, temperature and wind direction and speed. A P-3 mission typically lasts 8 to 10 hours. NASA's HS3 mission used the Global Hawk, a high-altitude long-endurance aircraft able to fly for 26 hours, to study hurricanes. As of November 2026, the Air Force flies a modified Lockheed C-130 called the WC-130J Super Hercules as its hurricane-hunting plane. As of November 2026, the NOAA Gulfstream IV jet has flown missions around nearly every Atlantic-based hurricane that threatened the United States since 1997.

Balloons and satellites widened the view. A radiosonde is a small, expendable instrument package that weighs 60 to 80 grams and hangs below a weather balloon; it reports pressure, temperature, humidity and GPS position every second and can rise higher than 35 km (about 115,000 feet). On April 1, 1960, NASA launched TIROS-1, the first successful weather satellite. In 1975 the SMS series became the first operational Geostationary Operational Environmental Satellites, called GOES, which orbit 22,236 miles above Earth's equator at the speed of Earth's rotation, so each keeps watching the same area. As of November 2026, a GOES imager can take pictures of weather patterns, hurricanes and severe storms as often as every 30 seconds. Polar-orbiting satellites fly over a storm approximately twice a day at a lower altitude than the satellites that stay in view.

A pattern found in NSSL Doppler radar data was named the Tornado Vortex Signature; it appears several kilometers above the ground before a tornado touches the ground, and this discovery led NOAA to build a nationwide network of Doppler radars. The Tornado Intercept Project of 1975 began the National Severe Storms Laboratory's tradition of organized field experiments. The VORTEX project began in 1994 with the aim of explaining how tornadoes form. In VORTEX2, in 2009 and 2010, researchers deployed 10 mobile radars and 40 other instrumented vehicles, and they sampled 36 supercells and 11 tornadoes to learn about tornado strength, lifetime and behavior. Doppler radar shows wind motion, with red for a target moving away from the radar and green for a target moving toward it. Scientists call the rotation inside a supercell a mesocyclone when Doppler radar detects it.

Rating a tornado means working backward from its damage. The original Fujita scale's precise wind speeds were guesses that were not verified by science or engineering tests. In 1971, T. Theodore Fujita of the University of Chicago developed it to sort tornadoes by their intensity. The Enhanced Fujita scale began operating in the United States in February 2007. It starts from 28 damage indicators and estimates a three-second wind gust, so its wind speeds are estimates, not measurements. A tornado's size or shape does not tell you how strong it is. The National Weather Service is the only federal agency with authority to give official tornado EF scale ratings. Enhanced Fujita ratings EF0 and EF1 are called weak, EF2 and EF3 strong, and EF4 and EF5 violent, and an EF0 tornado, the weakest category, has gusts up to 85 mph (135 kph). Weak tornadoes usually last less than 10 minutes and have winds less than 100 mph (160 kph).

The hurricane scale had a different origin. Herbert Saffir, an engineer, conceived it in 1969, while working on a report for the United Nations, because there was no scale for storms like the well-known earthquake scales. He showed it to Robert Simpson, director of the National Hurricane Center, who began using the scale in 1973. The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based only on a hurricane's maximum sustained wind speed, and it does not include rain, flooding or storm surge. Category 3, the first major category, means sustained winds of 111 to 129 mph, and Category 5, the top of the scale, is sustained winds of 157 mph or higher.

The numbers set the two storms side by side. The average hurricane spreads across approximately 340 miles (547 km), far wider than any tornado. Some tornadoes are quite narrow, only approximately 250 feet (75 meters) across where they touch the ground, while others can be up to two miles across. A typical tornado travels at approximately 10 to 20 miles per hour, yet it can move from almost standing still to faster than 60 miles per hour. Tornadoes have been reported in all fifty states. As of November 2026, tornadoes have traveled approximately 3.5 miles along the ground on average, based on path length records since 1950. As of November 2026, approximately 1,200 tornadoes touch down in the United States each year. As of November 2026, approximately 75% of the world's tornadoes happen in the United States. As of November 2026, EF4 and EF5 tornadoes make up only approximately 2% of all tornadoes.

Words to know

• supercell: rotating thunderstorm
• latent: hidden
• Coriolis: spin effect
• radiosonde: balloon instrument
• intensification: getting stronger
• mesocyclone: rotating updraft