I've seen those when we used to fish offshore in my G'pa's boat off Hilton Head, SC. Everyone seems to take those very seriously. The first time we encountered one we were out fishing over an artificial reef and noticed that all the other boats had disappeared. Inquisitively, we turned the radio on and realized they were departing because of a water spout. We looked around and realized it was a mile away and headed toward our direction. Needless to say, we hightailed it 90 degrees to it's path. It was a bright sunny day with a few clouds out - it was weird.