What is a tropical wave?
Tropical waves, also known as easterly waves, are elongated low-pressure areas that cause cloudiness and thunderstorms. They form when warm air drifts off of Africa into the Atlantic Ocean, and they are usually pushed westward by prevailing winds. Tropical waves can often develop into tropical cyclones: 60% of all Atlantic tropical cyclones originate from tropical waves, and about 85% of Atlantic hurricanes of Category 3 or greater come from tropical waves. About 60 tropical waves form off of the African coast each year. Sometimes, tropical waves can have tropical-storm force winds (39-73 mph) without being considered tropical storms, since tropical storms must have closed circulation. Hurricane formation and its progression always begins with a tropical disturbance. Tropical disturbances can be tropical waves, but not always. The disturbance then develops into a tropical depression, which has a closed circulation. The system then forms into a tropical storm, before finally developing
