Hurricanes and tornadoes are studied with radar, aircraft and satellites, and some questions about them are open, so start with how a tornado forms. Rising air in a thunderstorm 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. Speed shear, a change in wind speed with height, is believed to be a key part of how rotating thunderstorm updrafts called mesocyclones 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 wall cloud that may produce a tornado can exist for 10 to 20 minutes before the tornado appears, but not always.

Hurricanes are forecast with many tools and some doubt. 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. 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. As of November 2026, predicting rapid intensification, when a hurricane quickly gets stronger, is a challenging problem for forecasters. 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 the rainbands, the more intense the storm tends to be.

Hurricanes are watched from the air and from space. 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. Hurricane hunter missions fly to locate the center of the storm and measure its central pressure and surface winds. Dropsondes dropped from the aircraft continuously send back pressure, humidity, temperature and wind direction and speed. On April 1, 1960, NASA launched TIROS-1, the first successful weather satellite. GOES satellites 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.

Tornado research built its tools in steps. A pattern found in NSSL Doppler radar data was named the Tornado Vortex Signature; 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, and in VORTEX2, in 2009 and 2010, researchers deployed 10 mobile radars and 40 other instrumented vehicles. 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, and when Doppler radar sees a large rotating updraft inside a supercell, forecasters call it a mesocyclone. On radar, the Tornado Vortex Signature appears several kilometers above the ground before a tornado touches the ground.

Ratings are a record of damage and wind. 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. Rating a tornado with the Enhanced Fujita scale starts from 28 damage indicators, and the scale estimates a three-second wind gust. Enhanced Fujita wind speeds are estimates, not measurements; they come from damage, and 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. An EF0 tornado, the weakest category, has gusts up to 85 mph (135 kph).

The numbers show how rare the strongest tornadoes are. The average hurricane spreads across about 340 miles (547 km), far wider than any tornado, and a hurricane's size is not a sign of how strong it is, while some tornadoes are quite narrow, only about 250 feet (75 meters) across where they touch the ground, and others can be up to two miles across. A typical tornado travels at about 10 to 20 miles per hour, but it can move from almost standing still to faster than 60 miles per hour. A tornado may be on the ground for an instant or for several hours, though the average is about five minutes. As of November 2026, EF4 and EF5 tornadoes make up only about 2% of all tornadoes. As of November 2026, about 1,200 tornadoes touch down in the United States each year. As of November 2026, tornadoes have traveled about 3.5 miles along the ground on average, based on path length records since 1950. Weak tornadoes usually last less than 10 minutes and have winds less than 100 mph (160 kph).

The hurricane scale has its own history. Herbert Saffir made a hurricane scale because there was no scale for storms like the well-known earthquake scales. He conceived it in 1969 and 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 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.

Words to know

• mesocyclone: rotating updraft
• intensification: getting stronger
• dropsondes: dropped probes
• radar: storm-seeing tool
• satellite: orbiting camera
• rotation: spinning