Hurricanes and tornadoes both spin, and forecasters read each one in its own way. Start with the tornado. Wind shear matters to a tornado. Directional wind shear is the change in wind direction with height. Rising air in a thunderstorm tilts rotating air from horizontal to vertical. Once the updraft rotates and is fed by warm, moist air at ground level, a tornado can form. Wind shear usually weakens a hurricane, but wind shear is always needed to make a tornado. A supercell is a long-lived, organized thunderstorm with a tilted, rotating updraft, a rising current of air. That updraft can be up to 10 miles wide and 50,000 feet tall. It can be there 20 to 60 minutes before a tornado forms.

Forecasters can 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 eyewall is a dense wall of thunderstorms surrounding the eye, and changes in its structure can change the wind speed. The spiral rainbands of a hurricane typically range from 50 to 300 miles long. The more curved the rainbands, the more intense the storm tends to be. A hurricane's size is not a sign of how strong it is. The average hurricane spreads across about 340 miles (547 km), far wider than any tornado.

Tornado ratings began in 1971, when T. Theodore Fujita of the University of Chicago developed a scale to sort tornadoes by their intensity. The original Fujita scale's precise wind speeds were guesses that were not verified by science or engineering tests. Rating a tornado with the Enhanced Fujita scale starts from 28 damage indicators. The scale estimates a three-second wind gust. Its wind speeds are estimates, not measurements, because they come from damage. 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. As of November 2026, EF4 and EF5 tornadoes make up only about 2% of all tornadoes.

The hurricane scale began with an engineer. Saffir made a hurricane scale because there was no scale for storms like the well-known earthquake scales. The idea was conceived in 1969 by engineer Herbert Saffir. He showed it to Robert Simpson, director of the National Hurricane Center. Simpson 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. It does not include rain, flooding or storm surge. Category 3, the first major category, means sustained winds of 111 to 129 mph. Category 5, the top of the scale, is sustained winds of 157 mph or higher.

Doppler radar shows wind motion. Red is a target moving away from the radar and green is a target moving toward it. 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. The VORTEX project began in 1994 with the aim of explaining how tornadoes form. A tornado watch means tornadoes are possible in and near an area. A tornado warning means a tornado has been seen or shown by radar.

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. A Hurricane Hunter mission in a P-3 plane typically lasts 8 to 10 hours. 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. 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.

Satellites gave forecasters a view from above. 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. 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. Polar-orbiting satellites fly over a storm about twice a day at a lower altitude than the satellites that stay in view. Satellites that circle the Earth watch tropical cyclones from the time they start until they fade.

Words to know

• intensity: strength
• shear: wind change
• mesocyclone: rotating updraft
• dropsondes: dropped probes
• geostationary: fixed in place
• indicators: clues