May 26 - July 31
Does Extratropical Transition Impact Tornado Production in Tropical Cyclones?
Neil Crosby and Benjamin S. Schenkel
What is already known:
- Most landfalling tropical cyclones produce tornadoes.
- About 50% of tropical cyclones undergo extratropical transition (ET).
- ET is associated with changes in tropical cyclone structure that likely alter tornado occurrence, but further investigation is necessary.
What this study adds:
- ET is associated with increased tornado frequency compared to non-ET cases.
- ETornadoes in ET cases are confined to the U.S. east coast, while non-ET tornadoes typically occur over the southern U.S.
- Tornadoes occur in the same cyclone-relative location for both ET and non-ET cases.
Abstract:
The conditions favoring tropical cyclone (TC) tornadoes are likely also present during extratropical transition (ET) including strong ambient deep-tropospheric vertical wind shear, sufficient convective-scale lower-tropospheric vertical wind shear, and thermodynamic instability, and supercellular convection. However, no previous studies have investigated how ET tornado occurrence may differ from the remainder of the TC lifespan. Hence, our objective is to investigate differences in tornado frequency and location between ET and non-ET TCs using tornado data, TC track data, and reanalysis-derived cyclone phase space data. These results showed that ET does increase 6-h tornado frequency compared to non-ET TCs. However, there was no change in the frequency of damaging tornadoes in ET versus non-ET cases. Regarding location, we found that tornadoes in ET cases are mostly confined to the U.S. east coast, while TC tornadoes widely occur in the southern U.S. These results are also consistent with the location of ET and non-ET TCs. Together, this research will provide the foundation for improving tornado forecasts in landfalling ET cases.