Examining Outer Band Supercell Environments in Landfalling Tropical Cyclones using Ground-Based Radar Analyses

Abstract

Supercells in landfalling tropical cyclones (TCs) often produce tornadoes within 50 km of the coastline. The prevalence of TC tornadoes near the coast is not explained by the synoptic environments of the TC, suggesting a mesoscale influence is likely. Past case studies point to thermodynamic contrasts between ocean and land or convergence along the coast as a possible mechanism for enhancing supercell mesoscyclones and storm intensity. This study augments past work by examining the changes in the hurricane boundary layer over land in context of vertical wind shear. Using ground-based single- and dual-Doppler radar analyses, we show that the reduction of the boundary layer wind results in a increase in vertical wind shear/storm relative helicity inland of the coast. We also show that convergence along the coast may be impactful to supercells as they cross the coastal boundary. Finally, we briefly document the changes in mesocyclone vertical vorticity to assess how the environmental changes may impact individual supercells.