Impact of warm sea surface temperature over a Kuroshio large meander on extreme heavy rainfall caused by an extratropical cyclone

On 12-13 April 2020, an extreme heavy rainfall event associated with an extratropical cyclone occurred over the eastern coastal region of the Kii Peninsula, Japan, when unusual warm sea surface temperature anomalies (SSTAs) over a Kuroshio large meander (KLM) was observed. Here, we carry out numerical experiments to examine the impact of the unusual SSTAs on this heavy rainfall event. The unusual warm SSTAs enhanced the low-level moisture that was transported toward the coastal region by the cyclone, resulting in an increase in precipitation. In particular, the maximum 3-hour precipitation is most affected by SSTAs compared with the maximum 1-hour and 24-hour precipitation. These findings suggest that the heat and moisture supply from the unusually warm SSTAs over the KLM affected the heavy rainfall event.