What is waterspout, which may have sunk luxury yacht off Sicily?

Italian officials believe a waterspout sank a luxury yacht with tech tycoon Mike Lynch and others onboard. A waterspout is a large column of air and mist that spins over a water body. Waterspouts usually form over warm ocean waters and can generate winds over 160 kmph. Tornadic waterspouts may begin as tornadoes over land and then move over water.