Does Extratropical Transition Impact Tropical Cyclone Tornado Environments?

Tornadoes that spawn from tropical cyclones (TCs) pose a threat to lives and property. Although nearly half of all TCs in the Atlantic Ocean undergo extratropical transition, there has only been one study investigating how tornado occurrence changes during transition. The present study conducts a climatological analysis of the impact of extratropical transition on synoptic, TC, and convective-scale parameters that may impact tornado occurrence in TCs from 1995--2020 by utilizing both observed TC data and radiosonde data. This study divided extratropical transition into three phases using the cyclone phase space: tropical (i.e., pre-transition), transition, and extratropical (i.e., post-transition). The results suggested that changes in tornado characteristics are associated with increases in synoptic-scale, deep-tropospheric (i.e., 850–200-hPa) vertical wind shear while TC intensity weakens and the extent of the outer wind field expands. Evaluation of radiosondes showed that the downshear right quadrant of the TC is the most favorable shear-relative quadrant for tornado occurrence, having the highest CAPE, lowest CIN, and greatest storm-relative helicity (SRH) values in all phases. Throughout transition, CAPE in this quadrant decreases and CIN remains the same. SRH in the downshear right quadrant increases at the beginning of transition and is followed by smaller decreases following transition corresponding with outer size changes and an increase in deep-tropospheric vertical wind shear. In the remaining three shear-relative quadrants, CAPE decreases as the lower troposphere becomes cooler and drier throughout transition, while CIN remains the same and SRH slightly increases.