Future changes in Hurricanes under Warmer Climate: Relative role of SST and Atmospheric Warming

Future changes in the hurricane track, intensity, and environmental conditions are studied over the Central–West Pacific region using a gray-zone regional Weather Research and Forecasting (WRF) model by applying the Pseudo Global Warming (PGW) technique. Three hurricanes (Gay, Nov 1992; Melissa, Sep 1994; and Nangka, Jul 2015) with long tracks from Central Pacific to West Pacific with varied intensity are selected for this study. Current climate simulations are conducted at 9km grid spacing using six different planetary boundary layer (PBL) and four different cloud microphysics (MP) parameterizations, showing larger sensitivity of the hurricane tracks (intensity) to the choice of PBL (MP) parameterization. With the UW PBL and the WSM6 MP parametrizations, all three hurricanes are simulated realistically with respect to the observed Best Track data. These hurricanes are then simulated under global warming scenarios using the PGW method. Climate perturbations are first calculated as the difference of the monthly mean variables (e.g., sea surface temperature, surface pressure, surface temperature, atmospheric temperature, relative humidity, and geopotential height) between the present (1990–2010) and future (2079–2099) climate conditions under the SSP5-8.5 scenario projected by 11 individual CMIP6 models and their multi-model ensemble mean. The climate perturbations for each variable are added to the hourly ERA5 initial and boundary conditions for each hurricane to provide the perturbed initial and boundary conditions for the future simulations. Diverse tracks and intensities are found in future climate simulations using the WRF-PGW approach. Among the 11 CMIP6 models, MIROC6 performs the best and is chosen for comparison with the current climate simulations. The MIROC6 future Tracks are longer but similar to the current climate for the first few days and then deviate northward compared to northwestward in the current environment. The longer lifetime for future hurricanes can be attributed to the warmer SST over northwestern Pacific. The increase in the wind speed in the latter half of the future storms is consistent with the warmer SST and the increase in the surface latent heat fluxes over northwestern Pacific. The increase in the latent heat flux provides positive feedback to the hurricane through ocean-atmosphere interactions and intensifies the storms. Although the warmer atmosphere might dominate the environmental impact during the hurricane's initial phases, increased atmospheric stability ultimately provides negative feedback to the hurricane's intensity. To test the above hypothesis, we further perform two additional experiments in which the impacts of SST warming and the changing atmospheric conditions are evaluated individually. These results will be presented with the aforementioned PGW experiments to understand the relative roles of SST and atmospheric warming on Central–West Pacific hurricanes in the future.