Nonsupercell Tropical Cyclone Tornadoes: Documentation, Classification and Uncertainties

This study builds upon recent work by the authors for closer investigation of a 2003–2011 subset of 85 tropical cyclone (TC) tornado events—out of 730 for which a convective mode could be assigned—that were not associated with identifiable supercellular structures. Environmental analyses for these events are offered from the Storm Prediction Center's (SPC's) hourly, gridded, three-dimensional environmental mesoanalysis database—consisting of objectively analyzed surface observations merged with Rapid Update Cycle (RUC) model analysis fields. Given their generally ambiguous velocity patterns, radar signatures for nonsupercell (NS) TC tornadoes are classified based mainly on reflectivity characteristics (discrete, clustered, quasi-linear, etc.). A wide variety of radar signatures have been found: some very ambiguous and not conformable to any particular archetype for convective structure, some needing correction for time and/or location errors, and some casting uncertainty on the existence of reported tornadoes in the absence of additional confirming documentation. Events are sorted by time of day, geography, damage rating, TC intensity at tornado time, and position with respect to the TC envelope. NSTC tornadoes generally tend to be shorter-lived, weaker in damage rating, and concentrated nearer to center than supercell events, but with considerable overlap in both spatial distribution and environmental parameter spaces.