Hurricanes classify as tropical or subtropical storms that form over open waters, have defined eyes, move in rotating motions and produce strong rain and winds. Hurricanes belong to the larger category of tropical cyclones, which includes tropical depressions and tropical storms, along with hurricanes. In the United States, hurricanes form in the Atlantic and Pacific oceans, along with the Gulf of Mexico.
Hurricanes, like other tropical storm systems, begin as tropical disturbances. They earn the classification of hurricane upon reaching wind speeds of 74 miles per hour. These hurricanes classify as Category 1 storms. All hurricanes produce wind and rain. Larger, stronger systems produce other severe weather, such as strong thunderstorms and even tornadoes. Hurricanes begin at sea and move towards landmasses. Some storms never reach the shoreline, while others make landfall. Hurricanes typically grow in size and strength upon progressing towards shore. They classify as Category 2 with wind speeds of less than 111 mph. Storms classifying as Category 3, 4 or 5 on the international Saffir-Simpson Hurricane Wind Scale, feature sustained winds greater than 111 mph. Storms may reach diameters of 400 to 500 miles and have eyes more than 20 miles wide. They require ocean water temperatures of at least 75 degrees Fahrenheit for survival, and weaken rapidly upon making landfall.