Waterspouts are in essence tornadoes that form over the ocean. The wind sucks the water up into the air, forming the classic water spout shape.
Waterspouts can form in any tropical water area, but primarily form around the southern coast of Florida. They can reach up to 22,000 feet high, depending on the cloud cover.
Most waterspouts are relatively small and short-lived, but they can reach large sizes of 90' in diameter or larger, with speeds up to 200mph.
Where tornadoes usually cause the most damage by flinging debris around, there is luckily little debris picked up by a water spout. However, it's always wise to stay clear of one, between the fast speed of the winds and the occasional driftwood piece that may have gotten caught up in one.
Tornados in general move about 30-40mph, and can move more quickly. This means that it is possible - although extremely unlikely - for a waterspout to catch up with and overtake a cruise ship. Even so, the ship's crew would most likely see the spout coming, and ask passengers to move inside, off the decks. It's unlikely that the ship itself would be seriously hurt by a brief encounter with the spout.
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