The impact of extratropical transition (ET) on tropical cyclone (TC) tornadoes is not fully understood with no prior tornado climatologies for ET cases. Hence, this study investigates how ET impacts tornadoes and convective-scale environments within TCs using multidecadal tornado and radiosonde data from North Atlantic TCs. This study divides ET into three phases: tropical (i.e., pre-ET), transition (i.e., during ET), and extratropical (i.e., post-ET). These results show that the largest portion of tornadoes occur before and during ET, with the greatest frequencies during ET. As TCs undergo and complete ET, tornadoes tend to shift geographically north and east, farther south or more strongly downshear right relative to the TC center, occur later in the day, and are more likely to be associated with greater damage. Evaluation of radiosondes showed that the downshear right quadrant of the TC is frequently the most favorable for tornado production, having the best combination of entrainment CAPE (ECAPE) and storm-relative helicity (SRH) values. Specifically, the downshear right quadrant shows slower decreases in ECAPE (associated with large-scale cooling/drying) and increased low-level shear/SRH through ET, relative to quadrants left of the deeptropospheric (i.e.., 850-200-hPa) vertical wind shear vector. These results have ramifications for the physical model and prediction of ET-related TC evolution, both in terms of their environment and subsequent hazard production Suggested Reviewers: