Future Changes in Tropical Cyclone Tornadoes
Substantial research has been done on future changes in tropical cyclone (TC) frequency, intensity, and precipitation. However, tornadoes associated with TCs have been understudied, despite the danger they pose. We investigated future changes in TC-tornadoes using ensembles of convection-permitting simulations with the pseudo-global warming or “storyline” approach. In particular, we studied four TCs that produced the greatest TC-tornado outbreaks on recent record in the U.S. We found robust increases in future TC-tornado activity for all four events (~1.5-4 times the historical) and a future increase in nocturnal TC-tornado activity for three of the four events. The future increases in TC-tornado activity were supported by enhanced thermodynamic and dynamic environmental favorability.
Future increases in total and nocturnal TC-tornado activity, together with an increasing coastal population, can lead to greater TC hazards in the future.
Tornadoes are a dangerous co-occurring extreme that can be produced by landfalling tropical cyclones (TCs). Substantial research has been done on future changes in TC frequency, intensity, and precipitation. However, it remains unknown how TC-tornado activity may change in the future. In this study, we investigated four TCs that produced the greatest TC-tornado outbreaks on recent record in the U.S. We performed four-member ensembles of convection-permitting regional climate model simulations representing each TC in the historical climate and a future climate for the mid-twenty-first century under a high greenhouse gas emissions scenario. The control simulations were hindcasts of the events under the synoptic conditions and mean climate in which they occurred. The future experiments applied the pseudo-global warming or “storyline” approach to represent the TC events if they were to occur in the future, by retaining the synoptic conditions but perturbing the climate state to a warmer climate using Energy Exascale Earth System Model (E3SM) simulations. Given that tornadoes are not resolved in the model, we used updraft helicity and radar reflectivity to identify potentially tornadic storms, or TC-tornado (TCT) surrogates. We found that the number of TCT-surrogates increased substantially (56–299%) in the future, supported by increases in most-unstable convective available potential energy, surface-to-700-hPa bulk wind shear, and 0-1-km storm relative helicity. Furthermore, nocturnal TCT-surrogate occurrence increased in the future for three of the four cases, which can pose an enhanced threat given that people are asleep and more likely to miss warnings at night. This research indicates that TC-tornadoes may become more frequent and a greater hazard in the future, compounding impacts from population growth and future increases in TC winds and precipitation.