Estimation of Maximum Wind Speeds in Tornadoes

A method is proposed for rapidly estimating the maximum value of the azimuthal velocity component (maximum swirling speed) in tornadoes and waterspouts. The method requires knowledge of the cloud-deck height and a photograph of the funnel cloud–data usually available. Calculations based on this data confirm that the lower maximum wind speeds suggested by recent workers (roughly one-quarter of the sonic speed for sea-level air) are more plausible for tornadoes than the sonic speed sometimes cited a decade ago. Comparison in a few cases with maximum wind speeds determined either by spray-tracking on motion pictures of a waterspout or by another method reported by the authors elsewhere (using the tephigram for air at the outer edge of the whirl) yields compatible results.