Suspicious clouds, for Dr. Avila, may mean a thunderstorm, full of wind and rain, forming in the tropics. Any one of a hundred clues, such as the way the clouds are defined or the intensity of a thunderstorm, might hint that a weather system contains the seeds of a major tropical storm, according to Dr. Avila. Tropical oceans are breading grounds for hurricanes. The tropics receive a great deal of sunlight, which warms the oceans and causes air and moisture to rise. This rising air can generate fierce thunderstorms, which may grow into even larger storms.
Thunderstorms can band together and grow into a proto-hurricane known as a tropical depression.
If the storm begins to spiral around a low pressure center, and the winds exceed 40 miles per hour, it is known as a tropical storm. If winds gust faster than 73 miles per hour, it becomes a hurricane. Most never strike land, but the few that do can be deadly and cause an estimated five billion dollars in property damage each year in the United States. If a major storm is developing, Dr. Avila can call out the Hurricane Hunters, an airforce unit based in Biloxi, Mississippi. The 53rd Weather Reconnaissance Squadron regularly flies into storms to obtain atmospheric measurements like wind speed, moisture levels, and pressure readings.