Atlantic Niño increases early-season tropical cyclone landfall risk in Korea and Japan

Tropical cyclones (TCs) in the western North Pacific (WNP), which occur mainly from June through November, are greatly influenced by El Niño-Southern Oscillation (ENSO), particularly during the peak and late seasons (August–November). However, during the early season (June–August; JJA), ENSO is in its onset or developing phase and thus is relatively weak. Consequently, the drivers of interannual variability in early-season WNP TC activity remain less understood. This study shows that Atlantic Niño/Niña, the leading mode of tropical Atlantic sea surface temperature variability in JJA, significantly influences early-season WNP TC activity. Specifically, Atlantic Niño produces anomalous upper-level convergence in the tropical WNP, resulting in a decrease in low-level relative vorticity and mid-level relative humidity in the southern WNP (0°–10°N), and an increase in low-level relative vorticity in the northern WNP (20°N–30°N). These environmental conditions lead to an increase in TC activity over the northern WNP and a decrease over the southern WNP. Due to the resulting northward shifts in TC genesis and track density, the risk of landfalling TCs in far eastern Asia, particularly Korea and Japan, is greatly increased. These results suggest that Atlantic Niño/Niña may serve as a key predictor for seasonal WNP TC activity, especially during ENSO-neutral years.