Hurricanes begin as tropical disturbances in warm ocean waters with surface temperatures of at least 80 degrees Fahrenheit. These low pressure systems are fed by energy from the warm seas. If a storm achieves wind speeds of 38 miles an hour, it becomes known as a tropical depression. A tropical depression becomes a tropical storm–and is given a name–when its sustained wind speeds top 39 miles (63 kilometers) an hour. When a storm’s sustained wind speeds reach 74 miles (119 kilometers) an hour it becomes a hurricane and earns a category rating of 1 to 5 on the Saffir-Simpson scale.