The Impact of Canonical and Non-canonical El Niño on Seasonal Tropical Cyclone Activity: High-resolution Tropical Channel Model Simulations

Tropical Pacific sea surface temperature (SST) variability characterized by the El Niño-Southern Oscillation influences seasonal Atlantic tropical cyclone (TC) activity, with El Niño generally suppressing Atlantic TCs. This study investigates how the location of maximum tropical Pacific warming during El Niño, which varies from the East Pacific (EP) to Central Pacific (CP), impacts seasonal TC activity and through what mechanisms, and is motivated by recent observed and projected future increases in the frequency of CP El Niño. Climate simulations are performed to supplement and clarify observationally based studies, which yield conflicting results because of a short data record that is complicated by Atlantic SST variability. Simulations are run with the WRF model configured as a tropical channel model at 27 km horizontal resolution. Monthly climatological SST is prescribed in the control simulation, and experiments are forced by tropical Pacific SST patterns characteristic of Central Pacific and East Pacific El Niño; each consists of 6 ensemble members. A statistically significant (5% level) reduction in Atlantic and increase in East Pacific seasonal (May-November) accumulated cyclone energy (ACE) is simulated in response to both the East Pacific and Central Pacific El Niño SST forcings despite weaker SST warming in the Central Pacific El Niño case. The simulated response in seasonal West Pacific ACE to both EP and CP El Niño is insignificant, although a shift in typhoon track density is simulated in response to EP El Niño.