tropical cyclone

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tropical cyclone (revolving storm) A generally fairly small but intense, closed low-pressure system which develops over tropical oceans. Wind speeds of at least 33 m/s (force 12 on the Beaufort scale, 64 knots or more) define such storms and distinguish them from less intense systems, e.g. tropical depressions (of twice or more than twice the diameter) or tropical storms. The atmospheric pressure gradient in such cyclones commonly ranges from about 950 mb at the centre to about 1000 mb at the margins.

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