A hurricane is a very strong storm that forms over the sea. It brings heavy rain, strong winds, and can cause a lot of damage when it reaches land. But how does a hurricane begin?
Hurricanes start over warm ocean water. The sea surface needs to be at least 26 degrees Celsius (about 79 degrees Fahrenheit) for a hurricane to form. Warm water heats the air above it. The hot air rises into the sky and creates an area of low pressure near the sea surface. More air around this low-pressure area begins to move in to replace the rising air. This new air also becomes warm and rises. As the warm, moist air goes up, it cools and forms clouds.
The rising air and clouds release heat energy. This makes the surrounding air lighter and rise even faster. The cycle continues: warm air rises, cooler air moves in, and more clouds form. Slowly, a large system of clouds and storms develops.
Because the Earth rotates, the moving air begins to spin. In the Northern Hemisphere, hurricanes spin counterclockwise. In the Southern Hemisphere, they spin clockwise. The faster the air spins, the stronger the storm becomes. If the winds reach 119 kilometers per hour (74 miles per hour), the storm is called a hurricane.
Over the ocean, a hurricane grows stronger because it keeps taking energy from the warm water. But when it moves over land or colder water, it loses energy and becomes weaker. Even so, hurricanes can still cause flooding, destroy houses, and endanger lives.
Hurricanes show us the great power of nature. By studying how they form, scientists can give warnings to protect people before the storm arrives.
