On the Mechanisms of the Active 2018 Tropical Cyclone Season in the North Pacific

The 2018 tropical cyclone (TC) season in the North Pacific was very active, with 39 tropical storms including eight typhoons/hurricanes. This activity was successfully predicted up to 5 months in advance by the Geophysical Fluid Dynamics Laboratory Forecast-Oriented Low Ocean Resolution (FLOR) global coupled model. In this work, a suite of idealized experiments with three dynamical global models (FLOR, Nonhydrostatic Icosahedral Atmospheric Model, and Meteorological Research Institute Atmospheric General Circulation Model) was used to show that the active 2018 TC season was primarily caused by warming in the subtropical Pacific and secondarily by warming in the tropical Pacific. Furthermore, the potential effect of anthropogenic forcing on the active 2018 TC season was investigated using two of the global models (FLOR and Meteorological Research Institute Atmospheric General Circulation Model). The models projected opposite signs for the changes in TC frequency in the North Pacific by an increase in anthropogenic forcing, thereby highlighting the substantial uncertainty and model dependence in the possible impact of anthropogenic forcing on Pacific TC activity.