Thermodynamic and Dynamic Contributions to Future Precipitation Changes for Atlantic TCs in Mid-Latitude Environments

When tropical cyclones (TCs) move over land, they can cause devastating damage to the areas they affect, especially in the form of heavy rainfall and associated flooding. In the future, there is strong consensus that TC rainfall will increase, though how the rainfall changes may differ for TCs in different synoptic environments has not been fully established. Previous studies that focus on rain rate changes for TCs over water or in tropical environments find that the main mechanisms driving these rain rate increases are thermodynamic in nature (i.e. increases in temperature, moisture, CAPE, etc.). However, for storms that move into more baroclinic midlatitude environments, these thermodynamic mechanisms are not the only ones contributing to high rain rates - dynamic mechanisms such as jet interactions and isentropic lift can provide additional forcing. Identifying which of these mechanisms dominate in future TC rain rate changes is important to understand how TCs in different synoptic environments will respond to climate change, and what that means for their impacts. Here we attempt to evaluate these mechanisms by analyzing three North Atlantic TCs that occurred in different synoptic environments: one purely tropical (Hurricane Florence, 2018) and two interacting with upper level jets, but with drastically different tracks (Hurricanes Floyd and Matthew, 1999 and 2016). We use the Weather Research and Forecasting model to simulate these storms in their respective present-day climates and then in a future, warmer, end-of-century climate using the Pseudo Global Warming method. All three storms exhibit increases in rain rates in the future but to varying degrees. The purely tropical TC saw the largest rain rate increases (34%) while the synoptic-interacting storms saw lesser increases of 21% and 23%. In analyzing the forcing mechanisms, we find that the thermodynamics dominate and the dynamics do not appear to be as important, at least within the limitations of our experimental design.