Analyzing the Evolution of Tornadic Environments in Landfalling Tropical Cyclones

Previous studies have analyzed various atmospheric tornado parameters in a Tropical Cyclone (TC) environment. This study focuses on the evolution of these parameters through a TC landfall. The TCTOR dataset, which assigns all TC tornadoes to their respective TC, is used to group qualifying events from a pool of 1201 tornadoes during the period of 1995-2010 into eight time intervals relative to TC landfall. The environment is then analyzed using seven operationally used tornado parameters. A statistical, spatial, and sounding analysis is performed to determine how the tornadic environment evolves over time after landfall. Analysis shows that statistically significant differences in the mean value of each parameter are found between pre-landfall, post-landfall, and various time interval comparisons. Composite field charts and case studies show that the wind shear parameters at different vertical layers help explain tornado concentrations in space at different time intervals. In addition, a comparison of composite field charts is made between the larger pool of 32 TCs in the ALL composite and the 10 TCs representing the lowest tercile, with respect to the total number of tornadoes produced. This comparison shows higher magnitudes of shear parameters in the ALL composite. Combined with model derived soundings of three prolific tornado producing TCs, this study shows that the increase in shear in the lowest layer (0-1 km) is the best diagnostic tool to explain the increase in tornado occurrences at TC landfall. This finding supports prior research, which showed that low level shear maxima coincided with tornado locations. The increase in shear in the 0-3 km and 0-6 km layers at later time intervals is found to be the best diagnostic tool to explain the secondary increase in tornado occurrences after 24 hours past TC landfall. Additionally, 24 hours after TC landfall appears to be the critical time that separates weaker TC tornadoes at prior time intervals from stronger ones that resemble mid-latitude cyclone tornadoes that occur after, based on parameter values, hodograph analysis, and conceptual models. Lastly, the Significant Tornado Parameter (STP), used with discretion, is shown to work well in diagnosing tornado occurrence in some time intervals but proves to be a poor tool in others.