Impact of El Niño-Southern Oscillation Phases on Tropical Cyclone Genesis in the Southwest Pacific: A Study of Seasonal and Decadal Changes (1971-2020

Tropical cyclones (TCs) are modulated by El Niño-Southern Oscillation (ENSO) on interannual timescales as ENSO impacts local Sea Surface Temperatures (SST) and atmospheric conditions, especially in the Pacific basin. The frequency, intensity, startup SST, windshear and life cycle of TCs vary between ENSO phases and TC seasons. Previous research focused on the Southwest Pacific (SWP) Basin has consistently shown that during El Niño phases TCs tend to form more towards the central Pacific, while during La Niña, their formation shifts towards the northeast coast of Australia. Also, TCs form more frequently during the late TC seasons than during the early TC seasons. Here, TC genesis is assessed using a Coupled ENSO index (using Niño 3.4 SST and the Southern Oscillation Index (SOI)) and a grouping into early (Oct-Jan) and late (Feb-May) TC seasons, in the decades from 1971 to 2020. We find that though the number of TCs in SWP are decreasing over the years, their SST at genesis and maximum wind speed are increasing, generating more intense TCs over the SWP basin. TCs formed during El Niño are more intense than those formed during La Niña even though there is no significant difference in their SST at genesis. We find that the threshold of environmental factors responsible for cyclogenesis in SWP are gradually changing, leading to more severe TC events in the region.