What Caused the Unprecedented Absence of Western North Pacific Tropical Cyclones in July 2020?

While the Atlantic basin experienced the busiest hurricane season in 2020, the typhoon activity over the western North Pacific (WNP) was also record-setting with no tropical cyclone (TC) formation in July 2020, which is the first time in available historical records. The unprecedented absence of TC formation is consistent with the extremely unfavorable large-scale conditions that are linked to an anomalous anticyclonic circulation over the WNP, which results mainly from sea surface temperature (SST) anomalies across the tropical oceans. Numerical experiments suggest that the tropical Indian Ocean SST anomalies, which were warmest in July 2020 since 1965, play a dominant role in the anomalous WNP anticyclonic circulation, while the increased zonal SST gradient across the tropical Pacific and the Atlantic SST warming also have important contributions. This study suggests that the configuration of SST anomalies across the tropical basins is quite important to the WNP TC activity. Plain Language Summary About four tropical cyclones (TCs) form every July in the western North Pacific (WNP), exerting significant societal and economic impacts on the Asian islands and coastal regions. However, no TCs formed in July 2020, which had never happened in historical records. The unprecedented absence of TC formation indicates its possible unique driving factors. It is found that the unprecedented absence is mainly linked to the extremely unfavorable large-scale conditions that are associated with an anomalous anticyclonic circulation over the WNP, which was driven by trans-basin sea surface temperature anomalies across the tropical oceans. The tropical Indian Ocean experienced the highest SST in July 2020 since 1965, thus we argue that the record-breaking Indian Ocean SST, coupled with tropical SST over the Pacific and the Atlantic, is a plausible cause for the unprecedented absence of typhoon formation in July 2020. These results suggest a crucial role of sea surface temperature distribution across the tropical oceans in WNP TC formation and thus can provide some instructive implications for understanding variations in the WNP TC activity. Key Points No typhoon occurred in July 2020, which is the first time in historical records The unprecedented absence of typhoon is linked to the extremely unfavorable large-scale conditions The unprecedentedly unfavorable large-scale conditions are mainly driven by sea surface temperature anomalies across the tropical oceans

Automated summary

No typhoon occurred in July 2020 in the WNP, which is attributed to sea surface temperature anomalies across tropical oceans.