This study examined explosively developing extratropical cyclone activity in the vicinity of Japan in boreal winter from 1979/1980 to 2016/2017 mainly using the Japanese 55‐year Reanalysis data. The in situ observation and reanalysis data revealed increased frequencies of both strong winds and heavy precipitation in Hokkaido, the northernmost island of Japan, after the end of the last century, which is consistent with the fact that the cyclones migrating along the Kuroshio Current (KC cyclones) have tended to approach the Hokkaido region in recent years. To examine factors controlling the cyclone track and rapid development, we performed composite analyses of the northwards migrating type (N type) and eastwards migrating type (E type) KC cyclones. In the N‐type cyclone, wave trains prevailed along the polar front and subtropical jets over the Eurasian continent, thereby forming an upper‐level trough (ridge) to the west (east) of the cyclone. An upper‐level divergence accompanied by rapid development of the N‐type cyclone excited wave packets downstream as a Rossby wave source, leading to further reinforcement of the upper‐level ridge east of the cyclone. The anomalous anticyclone with a barotropic nature is capable of forcing the cyclone track to shift northwards. Furthermore, a combination of the N‐type cyclone and the anomalous anticyclone to its east facilitates moisture import into the cyclone system from lower latitudes, contributing to enhanced moisture flux convergence. In reality, diabatic heating in the vicinity of the cyclone centre is larger in the N‐type cyclone than in the E‐type one. It is also suggested that the pronounced Rossby wave propagation along the subtropical jet related to a climate regime shift in the Tropics is responsible for the recent increase in the number of N‐type cyclones.

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Using the Database for Policy Decision-Making for Future Climate Change (d4PDF), this study examined the impact of a tropical climate regime shift around 1998/1999 on explosive cyclone activity around Japan in boreal winter, highlighting cyclones moving along the Kuroshio Current (KC cyclones), especially northward-migrating (N-type, as defined in Tsukijihara et al., 2019) KC cyclones. Wave-train patterns along the Asian jet affect the track and rapid development of N-type cyclones, and the frequency of the top 10% of pronounced wave-train patterns using a teleconnection index (NI10%) has increased since 1998/1999. Tropical precipitation in the region close to the Bay