Abrupt enhancement of convective activity over the subtropical western North Pacific around 20°N, 150°E is known as the convection jump (CJ) caused by the ocean–atmosphere coupling, which is one of the important factors inducing the end of the Baiu season in Japan. Using atmospheric reanalysis and observation data for 1974–2021, this diagnosis is made for the influences of Rossby wave propagation and breaking, high-potential vorticity (PV) intrusion, and cutoff lows over the western North Pacific on CJ occurrence.

Preceding CJ occurrence, southeastward Rossby-wave propagation is discernible along the upstream of the mid-Pacific trough in the upper troposphere, and its energy accumulates over the northeast of the CJ region. The subsequent wave breaking near the exit region of the Asian jet induces the southwestward intrusion of high-PV airmass toward the northeast of the CJ region, which is concurrent with the enhancement of convective activity. The high-PV intrusion may also be interpreted as westward-moving, upper-level cutoff lows migrating from the mid-Pacific trough. The diagnosis of Q-vector indicates that variations in the extratropical upper-tropospheric circulation induce dynamical ascent, contributing to the onset and maintenance of convective activity over the CJ region. Moreover, the PV budget analysis suggests that the persistent positive advection of PV at the edge of the high-PV intrusion nearly counterbalances the intense low-PV generation by diabatic heating associated with the CJ. These results indicate that the CJ is influenced by extratropical upper-tropospheric variations as well as the coupled atmosphere–ocean system in the subtropical western North Pacific.