CORPUS CHRISTI, Tx — A waterspout is a cyclonically rotating column of air attached to a thunderstorm or a towering cumulus and in contact with the water below, be it a lake or ocean. Waterspouts come in two varieties: 1) “fair weather” and 2) tornadic. Either can pose a hazard to mariners or beachgoers, so we need to pay attention.
On Wednesday, Oct. 16, a strong cold front moved through the Coastal Bend and adjacent coastal waters during the morning hours, and it induced a spate of showers and thunderstorms. Those storms generated multiple waterspouts, beautifully photographed by our local residents.
Fair weather waterspouts occur when there are light winds but strong low-level instability, and that generates a condition that involves vertical acceleration of warm, unstable air. The atmosphere most efficiently lifts this air as a rotating column, resulting in the waterspout. This kind of waterspout can drop from a towering cumulus cloud or a thunderstorm.
Tornadic waterspouts form in much the same way as over-land tornadoes: in an environment of strong vertical wind shear and instability. Such was the case last Wednesday, when a potent cold front moved through the region. The front brought very strong east northerly low-level winds, with west and northwesterly flow above. The front created lift needed for the thunderstorms and the vertical wind shear generated mesocyclones to form the waterspouts.
Both kinds of phenomena can be dangerous, and when the National Weather Service suspects a storm may be generating a waterspout, or when one is reported, they will issue a Special Marine Warning. Boaters and beachgoers are advised to seek shelter from waterspouts the same as they would from tornadoes. In fact, if a waterspout moves over land, by definition it becomes a tornado.