Hurricane and tropical cyclone tornado environments from RUC proximity soundings (Formerly P8.1)

Several studies have examined thermodynamic and kinematic characteristics of landfalling tropical cyclone environments associated with shallow supercells and tornadoes using observed and simulated soundings. With high resolution model soundings available to forecasters in recent years as estimates of near-storm environment, a study based on operational model-derived profiles associated with tropical cyclone tornado settings has been absent, but seems desirable.

This empirical study uses 109 Rapid Update Cycle (RUC) analysis soundings associated with 21 landfalling tropical cyclones along the Gulf and Atlantic coasts of the United States from June 2001 through June 2006 to examine common parameters used in assessing supercell tornado environments. Of these profiles (most in the right front quadrant), 41 were associated with nontornadic tornado-warned storms, and 68 were associated with tornadic storms.

Results suggest that, when using operational RUC-derived parameters, tropical cyclone environments more effective in producing tornadoes tended to have larger convective available potential energy (CAPE) and stronger deep layer shear in the right front quadrant. When considering significant tornadoes (F2+ intensity), 0-1 km storm-relative helicity (SRH) tended to be larger, resulting in stronger combinations of CAPE and low-level SRH. In other words, many of the same parameters associated with non-tropical supercell tornado environments worked reasonably well in distinguishing tropical cyclones that were relatively prolific tornado producers in their right front quadrants from those that were not. This was in spite of the fact that buoyancy was shallower in the vertical compared to many warm season non-tropical supercells, as documented by other hurricane tornado studies.

It was also found that, given the very moist and humid low-level conditions that limit low-level mixing and dilution of buoyancy in tropical cyclones, lifted parcels from mixed layer depths shallower than the lowest 100 mb were generally more representative of available buoyancy in such environments. The above results will be documented and discussed.