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Oceanic eddies populated in the western boundary current regions in the midlatitude have been found to exert significant influence on atmospheric boundary layer, storm tracks, and large-scale atmospheric circulation. However, mechanisms governing how mesoscale sea surface temperature (SST) anomalies associated with oceanic eddies affect extratropical cyclogenesis remains unclear. Here, we investigate the influence of Kuroshio oceanic eddies on cyclogenesis in the North Pacific in high resolution climate model simulations using a cyclone tracking approach. Based on cyclone tracking and composite analyses, we find that presence of mesoscale SST anomalies almost doubles water vapor supply, leading to significant increase of diabatic heating release and eddy potential energy to eddy kinetic energy conversion and thus supporting stronger storm growth rate and intensified cyclones. This finding implies that moisture process is the key linking mesoscale oceanic eddies in the western boundary current regions with storm tracks in the midlatitude.

Plain Language Summary Extratropical cyclones transport tremendous amount of heat and moisture poleward in the midlatitude and are important for climate variability. Mesoscale oceanic eddies, circulations with horizontal scales of hundreds kilometers, rich in the frontal regions are found to potentially influence atmospheric storm track and extratropical cyclones. However, the dynamics behind remains unclear. By identifying and tracking cyclones in high-resolution model simulations, we demonstrate that the presence of mesoscale oceanic eddies in the Kuroshio region can support stronger storm growth rate and intensified cyclones with shorter life cycle. We also provide direct evidence for the modification effect of mesoscale oceanic eddies on water vapor, heat release, and energy conversion during cyclone development. The findings have important implications for improving extratropical cyclone forecasts and climate prediction in the midlatitude.