When lightning flashes, the thunder reaches you a few seconds later: sound needs about 3 seconds per kilometer (5 seconds per mile). Watch for the Boom! in the card below.
Key: orange dots = warm, moist air rising; blue dots = cold air sinking; teal = moist air flowing in. The EF and Saffir-Simpson ranges are the official ones (NWS and the National Hurricane Center). Sizes, heights, the hurricane’s strength from ocean temperature and the storm surge are simplified teaching values, not a forecast.
Light reaches you almost instantly; thunder travels at the speed of sound, about 343 m/s. Start a practice storm. The timer starts at the flash; press the button the moment you hear (or see) the thunder.
A watch means the weather could turn dangerous: be prepared. A warning means it is happening or about to: take action now. Decide for each alert.
Forecasters plot a hurricane’s center every few hours from satellites, aircraft and radar. These are the official best-track positions of Hurricane Ian from the National Hurricane Center. Tap the map at each latitude and longitude to plot the track (within about 1°), or let the page plot it. The dots are colored by strength. On a phone, swipe the map sideways.
| # | Time | Lat | Lon | Wind | Strength |
|---|
Data: National Hurricane Center Tropical Cyclone Report for Hurricane Ian (AL092022), best track at 12 UTC each day plus three of its landfalls (Cuba, Cayo Costa in Florida, South Carolina; it also crossed the Dry Tortugas and made a second Florida landfall near Punta Gorda); wind = maximum sustained wind, 1 kt = 1.15 mph. Hurricanes affect real communities; forecasters track them so that people can prepare and leave in time.
Cut a hurricane in half and this is what you would see. Pick Basic (7 labels) or Advanced (12), then try the blank diagram, the label quiz and match the jobs. On a phone, swipe the diagram sideways.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back.
Each line describes the job of one part. Tap a part name, then tap the box next to the job it does. Tap a filled box to take the word back.
Tap a card, then press Place here on the box it belongs in. Press Check when all 12 are placed.
A full worksheet with an answer key: label the hurricane cross-section, tornado or hurricane, watch or warning, rate storms on the official EF and Saffir-Simpson scales, lightning distance and the thunderstorm stages, the Hurricane Ian track, and explain-and-plan questions (high school: wind force and forward speed). The label part uses the level chosen in the diagram above.
Meteorologists use several units: knots (kt) at sea and in aviation, mph in US warnings, km/h and m/s elsewhere. The Saffir-Simpson scale uses a hurricane’s maximum sustained wind; the EF scale uses a tornado’s estimated 3-second gust.
Distance on a sphere (haversine, Earth radius 6,371 km). One degree of latitude is about 111 km; a degree of longitude shrinks by cos(latitude).
A thunderstorm needs three ingredients: moisture, unstable air (air that keeps rising once it starts) and something to lift it, such as a cold front, a mountain or ground heated by the Sun. Rising air cools and its water vapor condenses into a cumulus cloud. In the developing stage there are only updrafts. In the mature stage rain and hail drag cold air down in a downdraft, the cloud reaches the top of the troposphere and spreads into an anvil, and lightning, heavy rain, hail and strong gusts are most likely. In the dissipating stage the downdraft cuts off the warm, moist air and the storm dies, but lightning can still strike.
Lightning is a giant spark between charged parts of a cloud, or between the cloud and the ground. It heats the air in its channel to as much as about 50,000 °F in a split second; the air expands so fast that it makes the sound of thunder. Light arrives almost instantly but sound takes about 5 seconds per mile (3 seconds per kilometer), so count the seconds and divide. Thunder can usually be heard only about 10 miles away: if you can hear it, you can be struck. “When thunder roars, go indoors,” and wait 30 minutes after the last thunder.
When the wind changes speed and direction with height (wind shear), the air between the slow and the fast wind starts to roll like a rolling pin. A strong updraft tilts this spinning air upright, so the storm’s updraft rotates: a mesocyclone, and the storm is a supercell. Under some supercells a lowered, rotating wall cloud forms and a tornado reaches down to the ground. Doppler radar can see the rotation, which is how many tornado warnings are issued. After the storm, surveyors rate the tornado on the Enhanced Fujita scale (EF0 to EF5) from the damage.
Over warm tropical oceans, evaporation loads the air with water vapor. When this air rises in thunderstorms, the vapor condenses and releases latent heat, which warms the air and makes it rise faster, lowering the pressure at the surface so even more moist air flows in. Earth’s rotation (the Coriolis effect) turns the inflowing air, so it circles counterclockwise in the Northern Hemisphere and clockwise in the Southern; this is also why hurricanes almost never form right at the equator. The storm organizes into a calm eye of sinking air (usually 30–60 km across), a ring of tall eyewall clouds with the strongest winds, and spiral rain bands. Strong wind shear tears young storms apart; over land or cool water they lose their fuel. The Saffir-Simpson scale rates the wind (Category 1 to 5), but along the coast the storm surge and large waves are the greatest threat to life, and inland it is usually flooding.
A blizzard is snow with sustained winds or frequent gusts of 35 mph or more that cut visibility to a quarter mile or less for at least 3 hours. Flash floods can rise in minutes: 6 inches (15 cm) of fast water can knock an adult over and 12 inches (30 cm) can carry away most cars, so “Turn Around, Don’t Drown.” Forecasters use Doppler radar, weather satellites, weather balloons and aircraft that fly into hurricanes, and they issue watches (be prepared) and warnings (act now). Engineers reduce the damage with safe rooms, stronger building codes, raised houses, sea walls and warning sirens.
In the hurricane scene, cool the ocean below 26.5 °C, then warm it to 30 °C and add strong wind shear. Cut the storm in half to see the eye, then make landfall and watch the storm surge. In the tornado scene, compare EF1 and EF4 damage, then press How does the spin start? Finally, plot Hurricane Ian and work out how fast it moved.
| Rating | Estimated 3-second gust | Example damage |
|---|---|---|
| EF0 | 65–85 mph (105–137 km/h) | Shingles and gutters off, branches broken |
| EF1 | 86–110 mph (138–177 km/h) | Roofs badly stripped, windows broken, mobile homes overturned |
| EF2 | 111–135 mph (179–217 km/h) | Roofs torn off well-built houses, large trees snapped |
| EF3 | 136–165 mph (219–266 km/h) | Whole stories of well-built houses destroyed |
| EF4 | 166–200 mph (267–322 km/h) | Well-built houses leveled, cars thrown |
| EF5 | over 200 mph (over 322 km/h) | Strong houses swept off their foundations |
Source: NWS Storm Prediction Center. The winds are estimates made from the damage, not measurements.
| Category | Maximum sustained wind | Damage |
|---|---|---|
| 1 | 74–95 mph · 64–82 kt · 119–153 km/h | Some damage: roofs, siding, big branches; power out for days |
| 2 | 96–110 mph · 83–95 kt · 154–177 km/h | Extensive damage: major roof damage, many trees uprooted |
| 3 (major) | 111–129 mph · 96–112 kt · 178–208 km/h | Devastating: roof decking lost, many trees snapped |
| 4 (major) | 130–156 mph · 113–136 kt · 209–251 km/h | Catastrophic: most of the roof and some walls lost |
| 5 (major) | 157 mph or more · 137 kt or more · 252 km/h or more | Catastrophic: many framed homes destroyed |
Source: National Hurricane Center. Below 74 mph the storm is a tropical storm (39–73 mph) or a tropical depression (38 mph or less). The category does not include storm surge or rain.
| Alert | Means | Examples | What to do |
|---|---|---|---|
| Watch | Conditions are favorable; the hazard is possible | Tornado Watch (usually 4–8 hours); Hurricane Watch (about 48 hours before tropical-storm-force winds) | Be prepared: review your plan, charge your phone, keep listening |
| Warning | The hazard is happening, about to happen or expected | Tornado Warning (radar shows rotation or a spotter sees a tornado); Severe Thunderstorm Warning; Flash Flood Warning; Hurricane Warning (about 36 hours ahead) | Take action now: shelter, or leave if told to evacuate |
| Advisory | Less serious weather that is still a nuisance | Flood Advisory, Wind Advisory | Take care, especially when traveling |
A tornado is a narrow, violently rotating column of air that reaches from a single thunderstorm to the ground. It is usually less than a few hundred meters wide and lasts minutes, but its winds can exceed 200 mph. A hurricane is a huge rotating storm system, hundreds of kilometers across, made of many thunderstorms. It forms over warm ocean water, has a calm eye, lasts for days and brings storm surge, flooding rain and widespread wind damage.
Key takeaway: tornadoes are small and short; hurricanes are huge and last days.Thunderstorms need moisture, unstable air that keeps rising once it starts, and something to lift the air, such as a front, a mountain or heating by the Sun. Rising air cools and its water vapor condenses into a towering cumulonimbus cloud. A storm goes through three stages: developing (updrafts only), mature (updrafts and downdrafts with heavy rain, hail and lightning) and dissipating (the downdraft takes over).
Key takeaway: moisture, unstable air and lift.Count the seconds between the flash and the thunder. Divide by 5 to get the distance in miles, or by 3 to get kilometers, because sound travels about 343 meters per second and light arrives almost instantly. For example, 15 seconds means about 3 miles (5 km). If you can hear thunder at all, you are close enough to be struck, so go indoors and wait 30 minutes after the last thunder.
Key takeaway: seconds ÷ 5 = miles; seconds ÷ 3 = kilometers.Most strong tornadoes come from supercells, thunderstorms with a rotating updraft. Wind shear, winds that change speed and direction with height, sets the air rolling horizontally; a strong updraft tilts this spinning air upright into a rotating column called a mesocyclone. Under some mesocyclones, a tornado forms and reaches the ground. Scientists still study exactly why some supercells make tornadoes and others do not.
Key takeaway: wind shear plus a strong updraft makes a rotating storm.The EF scale rates tornadoes from EF0 to EF5 using the damage they cause. Surveyors look at what was damaged and how badly, and estimate the 3-second gust: EF0 65–85 mph, EF1 86–110, EF2 111–135, EF3 136–165, EF4 166–200 and EF5 over 200 mph. It replaced the original Fujita scale in the United States in 2007.
Key takeaway: it estimates the wind from the damage.The Saffir-Simpson Hurricane Wind Scale rates a hurricane from Category 1 to 5 by its maximum sustained wind: Category 1 is 74–95 mph, 2 is 96–110, 3 is 111–129, 4 is 130–156 and 5 is 157 mph or more. Category 3 and above are major hurricanes. The scale only describes the wind; it does not include storm surge, rainfall flooding or tornadoes, which can be deadly even in a weaker storm.
Key takeaway: categories rate the wind only.Storm surge is an abnormal rise of the sea pushed onto the coast by a storm’s winds. With large waves on top, it can flood whole neighborhoods within minutes, sweep buildings away and cut off escape routes. The National Hurricane Center says storm surge and large waves pose the greatest threat to life and property along the coast. Its height depends on the storm’s strength, size and speed and on the shape of the coast and sea floor.
Key takeaway: storm surge is the deadliest part of a hurricane on the coast.A watch means conditions are favorable for the hazard, so it could happen: be prepared and keep listening. A warning means the hazard is happening, is about to happen or is expected: take action now. For example, a Tornado Watch often covers a large area for 4 to 8 hours, while a Tornado Warning is issued when radar shows strong rotation or a spotter sees a tornado, and usually lasts about 30 minutes for a much smaller area.
Key takeaway: watch: be prepared; warning: act now.Go to a basement, safe room or a small interior room on the lowest floor, away from windows, and cover your head. At school, follow your tornado drill and stay out of large rooms such as gyms and cafeterias. Mobile homes, sheds and cars are not safe; get to a sturdy building if you can. Do not wait to see the tornado before you act.
Key takeaway: lowest floor, interior room, away from windows.It shows the real processes: updrafts and downdrafts in a thunderstorm, the time delay of thunder, a supercell with a rotating wall cloud, the official EF and Saffir-Simpson wind ranges, a hurricane’s eye, eyewall and rain bands circling the right way in each hemisphere, and Doppler radar showing rotation. But it is a teaching model: sizes and heights are not to scale, and the hurricane’s strength from ocean temperature and the storm surge heights are simplified example values. The Hurricane Ian track uses real National Hurricane Center data.
Key takeaway: real processes and official scales, simplified numbers.