Decreasing Quiescence of Tropical Cyclones in the Western North Pacific

Due to less tropical cyclone (TC) occurrences, the climatology of the quiescent TC season (i.e., March-April-May, MAM) in the western North Pacific (WNP) is less understood when compared to the more active season (i.e., June-November). Here we show observational evidence of significantly decreasing TC quiescence during MAM that can be attributed to more Central Pacific El Niño events from 2002 to 2022. A Central Pacific El Niño is related to an asymmetric sea surface temperature (SST) pattern where warm (cool) SST anomalies are concentrated in the central (western) Pacific, which consequently contributes to the overall decrease in TC quiescence in MAM. Such anomalous SST pattern prompts the western North Pacific Subtropical High to expand westward, creating a conducive large-scale environment for TC development and allowing TCs to move closer to the landmass, which ultimately leads to an increasing cost of TC-associated damages during the quiescent season. Our study provides new insights into the decreasing TC quiescence and TC climatology in the WNP during MAM, which is ultimately expected to contribute to disaster risk reduction in the region.