资源环境科技发展态势分析平台

Northern Hemisphere tropical cyclone (TC) genesis (TCG) frequency in June-September of 2018 reached a record high since 1965. This unprecedented TCG was mainly driven by the North Pacific (NP) and the subtropical North Atlantic (NA). TCs in the western North Pacific (WNP) predominately took a northward-recurving track, resulting in the highest number of named storm days in the subtropical WNP on record. TCs in the eastern North Pacific propagated anomalously westward with three Category 4-5 hurricanes reaching the central North Pacific. The unprecedented TCG in the NP was caused by a persistent weakening of the NP subtropical high that was tightly coupled with the subtropical NP sea surface temperature (SST) warming. In the NA, enhanced TCG was mainly found in the subtropics owing to a favorable large-scale environment forced by subtropical SST warming. The result here has important implications for understanding variability in TC activity on the hemisphere-scale.

Plain Language Summary The Northern Hemisphere (NH) has about 60 tropical cyclones (TCs) every year, which account for about 70% of the global total and exert significant societal and economic impacts on islands and coastal regions. In 2018, 20% more TCs (i.e., 72 TCs) were observed compared with the long-term average. This active TC genesis (TCG) mainly occurred in June-September over the North Pacific (NP) and the subtropical North Atlantic (NA), resulting in a record high since the satellite era began (1965 onwards). The unprecedented NH TCG was likely driven by subtropical sea surface temperature warming in the NP and the NA and an associated modulation of the large-scale environment important for TCG. These results suggest a crucial role of subtropical sea surface temperature in NH TC activity and thus can provide some instructive implications for understanding changes in TC activity on the hemisphere-scale.