Hurricanes gain strength from warm moist air rising from water in the tropics. These moisture-driven storms begin as low pressure areas that form over warm ocean waters in the summer and early fall, and gain strength and speed as winds within the low pressure zone organize into a rotation.
A hurricane begins as a tropical disturbance, which is a low pressure area over warm water characterized by thunderstorms and high humidity. A tropical disturbance can grow into a tropical depression if wind speeds within the system reach 38 miles per hour. Once wind speeds reach 39 miles per hour, the system can be classified as a tropical storm. Once wind speeds hit at least 74 miles per hour, a tropical storm is reclassified as a hurricane.
Although scientists don’t know exactly how or why a hurricane forms, they do know that a hurricane requires water temperatures of at least 79 degrees Fahrenheit. NASA can witness the formation of hurricanes with the use of satellites that capture images from space. Some of these satellites are used to measure cloud and ocean temperatures, wind speed and direction, and the volume of rain falling in the area of a tropical storm or hurricane.
There are five different categories of hurricanes. A category one hurricane, the least severe type of hurricane, features winds of up to 95 miles per hour and does the least damage to inland communities. A category five hurricane is the deadliest and can contain winds of up to 155 miles per hour.