16. What is a waterspout and what causes it? 



A waterspout is a funnel-shaped column or spout of water extending 

 from the sea to a cloud and sustained by a circular wind movement. 



Waterspouts result from meteorological causes. Atmospheric con- 

 ditions associated with waterspouts are unstable. The air temperature 

 may be much lower than the sea surface temperature. Thunder and 

 lightning often accompany the phenomenon. They occur most fre- 

 quently in the tropics, but are also known in temperate zones. 



The occurrence and movement of waterspouts are unpredictable. 

 They may occur in gales or calms, move with or against the winds, ro- 

 tate either clockwise or counterclockwise, and move slowly or rapidly. 

 Winds in the most severe spouts may exceed 200 miles per hour. 



Heights from 10 to 5,000 

 feet and widths from 10 to 

 500 feet have been reported. 



On June 25, 1964, meteor- 

 ologists had an opportunity 

 to observe waterspouts at 

 close range at the Tampa air- 

 port. At the time meteoro- 

 logical conditions were very 

 unstable, and severe thunder- 

 storms had occurred just before the spouts were observed. The sustained 

 measured wind speed was 67 miles per hour, with gusts of 79 miles per 

 hour. During this period, 1-3/4 inches of rain was recorded in 40 min- 

 utes, accompanied by hail. The total distance covered by the spouts was 

 about 10 miles; the average speed of advance of the waterspouts was 

 30 miles per hour. 



Miller, Robert C. 



The Sea, Random House, 1966. 

 U. S. Naval Oceanographic Office 



Science and the Sea, Washington, D. C, 1967. 



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