Record warmth in the Sea of Japan amplified the September 2024 Noto heavy rainfall associated with a mesoscale low-pressure disturbance

Abstract In September 2024, record-breaking rainfall caused severe flooding and landslides in the Noto region, Japan, where recovery from the devastating Noto Peninsula earthquake was still ongoing. During this event, the Sea of Japan experienced record warmth, with monthly-mean sea surface temperature anomaly of + 2.9 °C. To quantify the impact of this anomalous ocean warming on the heavy rainfall, we conducted numerical sensitivity experiments using a regional atmospheric model in which only the sea surface temperature conditions in the Sea of Japan were replaced with those from each year between 1991 and 2020. Simulated rainfall over the Noto region was nearly twice as large under the observed 2024 SST conditions, indicating that the exceptionally warm ocean substantially amplified the event. The warming did not alter the occurrence or track of a mesoscale low-pressure disturbance along the autumn rain front, but the intensity of the disturbance systematically increased with SST and was accompanied by stronger southwesterly winds and moisture transport into the frontal zone. Ocea​nic analyses further showed a marked strengthening of the Tsushima Warm Current in 2024. These results highlight the importance of atmospheric responses to anomalously warm ocean conditions in amplifying extreme rainfall under anomalously warm ocean conditions and underscore the need to consider such processes in future risk assessments around Japan.