Mid-Century Climate Change Impacts on Tornado-Producing Tropical Cyclones

Tornadoes are a co-occurring extreme that can be produced by landfalling tropical cyclones (TCs) in the United States. These tornadoes can cause loss of life and property damage in addition to the TC they were spawned from. There is considerable uncertainty about how the severe weather environments of landfalling TCs may change in a future climate state and how this could impact tornado frequency from TCs. In this study, we investigated four TCs that made landfall in the U.S. and produced large tornado outbreaks. We produced four-member ensembles of convective-allowing (4 km resolution) regional climate model simulations representing each TC in the historical climate and a mid-twenty-first century future climate. To identify potentially tornadic storms, or TC-tornado (TCT) surrogates, we used thresholds for three-hourly maximum updraft helicity and maximum radar reflectivity, as tornadoes are not resolved at the spatial resolutions used. We found that the ensemble-mean number of TCT-surrogates increased substantially (56–299%) in the future, supported by increases in most-unstable convective available potential energy, surface-to-700-mb bulk wind shear, and 0–1-km storm-relative helicity in the tornado-producing region of the TCs. On the other hand, future changes in most-unstable convective inhibition had minimal influence on future convective storms. This provides robust evidence that tornado activity from TCs may become more frequent in a future climate state. Furthermore, TCT surrogate frequency between 00Z and 09Z increased for three of the four cases, suggesting enhanced potential for nocturnal storms capable of producing tornadoes. All of these factors indicate that tornadoes from TCs may become more frequent in a future climate and may become a greater hazard as a result, compounding impacts from future increases in TC winds and precipitation.