Exploring Inland Tropical Cyclone Rainfall and Tornadoes under Future Climate Conditions through a Case Study of Hurricane Ivan

The overarching purpose of this study is to investigate the impacts of anthropogenic climate change on both tropical cyclone (TC) rainfall and the frequency of tornadoes spawned by tropical cyclones making landfall in the U.S. Atlantic Basin. Hurricane Ivan (2004), a prolific tropical cyclone tornado (TCT)-producing storm, is the particular case under consideration. Using the Weather Research and Forecasting model, Hurricane Ivan is simulated under its current-climate forcing. Such a control simulation is compared to simulations conducted using a “pseudo-global” warming (PGW) approach, which allows for an assessment of long-term impacts of changes in greenhouse gas concentrations and associated radiative forcing. The PGW simulations involve future climate conditions over the late (2080-2090) century period under representative concentration pathway (RCP) 8.5, using the Community Climate System Model version 4 (NCAR), Model for Interdisciplinary Research on Climate version 5 (MIROC), and Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL) climate models. Changes in TC intensity and TCT production, identified for the PGW-modified Ivan are documented and analyzed.

In lieu of explicitly resolving tornadoes, TCT surrogates (TCT-S) are identified using an algorithm based on a resolution dependent threshold of maximum updraft helicity and simulated radar reflectivity. Compared to the control simulation (CTRL), all three PGW simulations show an increase in TC intensity, as well as westward shifting tracks. The TCs under PGW also generate substantially more accumulated rainfall over the course of Ivan’s progression overland. Regarding TCT-S production, MIROC produced more TCT-Ss than the control, while the GFDL and NCAR models produced fewer TCT-Ss.