A hurricane is a big storm that forms over warm ocean water. Scientists also call it a tropical cyclone. A tropical cyclone is a hurricane when its winds reach 74 miles per hour. Hurricanes are called typhoons in the western North Pacific and cyclones in some other places. The Saffir-Simpson scale rates hurricanes from 1 to 5 by their wind speed. A hurricane has a calm, clear center called the eye.

Storm surge is sea water pushed onto land by the winds of a storm. Hurricanes usually get weaker when they move over land. Even so, hurricanes are not just a coastal problem, because rain and wind can reach far inland. Weather satellites watch hurricanes from high above Earth. If officials say to evacuate before a hurricane, go right away to a safe place.

A tornado is a spinning column of air that reaches from a storm cloud down to the ground. Experts rate a tornado by studying the damage it caused. The Enhanced Fujita Scale has six ratings, EF0 to EF5. EF0 is the weakest tornado rating, with wind gusts up to 85 mph, and EF5 is the strongest, with gusts over 200 mph. A tornado watch means tornadoes are possible in and near the area. A tornado warning means a tornado is near and it is time to move to a safe place. In a tornado warning, go to a small room with no windows on the lowest floor of a sturdy building.

An earthquake is an intense shaking of Earth's surface. Scientists use an instrument called a seismometer to measure the shaking waves from an earthquake. Aftershocks are smaller earthquakes that follow a larger earthquake in the same area. If the ground shakes, drop down, cover your head and neck, and hold on until the shaking stops.

An earthquake under the ocean can push the water above it and start a tsunami. A tsunami can also be started by a volcano in the ocean. Tsunamis travel very fast. In the deep ocean they can move as fast as a jet plane. A tsunami wave grows taller as it moves into shallow water near the shore. If the water pulls far back from the shore after an earthquake, a big tsunami may be on its way.

A flood is water that covers land that is usually dry. Floods can come from heavy rain, from fast-melting snow, or when ocean waves come on shore. A flood watch means a flood is possible. A flood warning means flooding is happening or will happen soon. Flash floods can happen within minutes of heavy rain and can come without warning. Just 6 inches of fast-moving flood water can knock a person over, and 12 inches can carry a car away. Never walk, swim or drive through flood water.

Weather forecasters send out warnings so people have time to get to a safe place. Communities send emergency alerts, so it helps to sign up for them. A NOAA Weather Radio with tone alert is one way a family can hear when a warning has been issued. A family can make a plan together for what to do in a disaster.

Words to know

• cyclone: spinning storm
• surge: pushed water
• inland: away from coast
• evacuate: leave for safety
• scale: rating system
• tsunami: big ocean wave