Impact of Unusually High SSTs in the Southern Part of the Sea of Japan on Heavy Rainfall That Occurred in Noto, Japan, on 21 September 2024

Numerical simulations were conducted to examine the influence of unusually high sea surface temperatures (SSTs) in the southern part of the Sea of Japan (SOJ) on heavy rainfall that occurred in Noto, Japan, on 21 September 2024. During this period, SSTs in the southern SOJ were significantly higher as compared to climatological normals. In a simulation in which local SSTs west of the Noto Peninsula were substituted with the climatological normals from 1991 to 2020, the maximum and area-averaged values of the 48-hour accumulated precipitation were reduced by approximately 28% and 14%, respectively, as compared with the control simulation. Backward trajectory analyses showed that boundary-layer air parcels entering the heavy rainfall region were enriched with substantial water vapor from the warm sea west of the Noto Peninsula. In addition, these parcels reached the heavy rainfall region without losing heat to the warm sea. These features indicate that the sensible and latent heat fluxes from the warm sea not only increase the water vapor content but also enhance low-level convective instability, leading to a significant increase in precipitation.