Peninsular Florida Tornado Outbreaks

Abstract

An analysis of statistics for 1448 tornadoes documented by the National Severe Storms Forecast Center from 1950 through 1994 at, or south of, 30° latitude in Florida was completed to determine the definition of a peninsular Florida tornado outbreak and develop a tornado outbreak climatology. A peninsular Florida tornado outbreak was defined as the occurrence of four or more tornadoes in 4 h or less. Thirty-five outbreak cases were identified. After a review of all available synoptic data for each case, they were categorized into three basic types: 1) those associated with extratropical cyclones (27 cases), 2) those associated with tropical cyclones of tropical storm or hurricane strength (5 cases), and 3) those associated with hybrid cyclones having both tropical and extratropical characteristics (3 cases). A detailed climatology covering spatial and temporal aspects of outbreak characteristics was completed. Mean severe weather indices, thermodynamic soundings, and hodographs were produced for each outbreak type. Case studies of each type of outbreak are presented to complement the climatology and mean environment information. It was found that tornado outbreaks account for 3.4% of all tornado days but caused 61% of all tornado deaths and 62% of tornado injuries. Most tornado deaths occurred in trailers or mobile homes. Extratropical outbreak tornadoes were most common from midmorning to early afternoon, while tropical outbreak tornadoes occurred mostly in the afternoon and evening. The outbreaks produced a much greater percentage of strong and violent tornadoes compared to the general tornado population. Hybrid outbreaks were the most consistently dangerous of the three types of outbreaks. Fundamental differences and similarities among the three outbreak environments are presented using mean soundings and case studies. The basic ingredients for tornado development in each type of outbreak were found to be the presence of strong low-level winds and shear, and enough instability to support thunderstorm development.