Decadal variability of tropical cyclogenesis and decay in the Southwest Pacific (#1053)
Of all natural hazards in the Pacific, tropical cyclones (TCs) are the most intense and frequent and represent a significant risk to the island nations of the Southwest Pacific (SWP). TCs are capable of causing significant impacts to properties, lives and infrastructure, accounting for approximately 76% of reported disasters. A particular challenge that island nations face is the inherent degree of variability in TC risk from season to season, which hampers adaptation planning. Therefore, the aims of this study were to review the historical variability of TC genesis and decay (i.e. the lifespan of the TC) and place any recent changes into perspective of the long-term variability. To achieve this, we evaluated the spatial distribution of genesis and decay over the last seven decades using the SPEArTC database for TCs that originate within 0°–35°S, 135°E–120°W. The results show substantial decadal variability in prime regions of genesis and decay from 1948 to 2017. In particular, we observe a significant displacement of TC genesis by 897.98km in east-northeast direction. Further, TCs appear to be decaying further east-southeast in recent decades, with significant displacement of 908.59km. We also observed that TCs undergoing extratropical transition have significantly decreased (in terms of frequency and duration) during the last four decades, however, the length of the extratropical cyclone (ETC) tracks have increased. We attribute these observations to conducive environmental conditions, including warmer sea surface temperatures (SSTs) in the eastern region of TC genesis, alongside sufficient relative humidity and favourable vertical wind shear. Further, the observed ocean warming and decreasing wind shear during recent decades towards the south of the SWP region favour the ETCs extension in an east-southeasterly direction. Significantly, the findings of this study increase our understanding of decadal to multidecadal TC risk for SWP island nations and may assist in improving seasonal TC outlooks.