Variability in tropical cyclone (TC) track morphology, as it evolves post genesis, presents continued challenges in accurately forecasting TC movement. Therefore, an improved understanding of TC track climatology is essential, given that TCs are one of the most critical natural hazards in the southwest Pacific (SWP) region. We examine the historical variability of TC tracks within the SWP over the last 70 years (1948-2017) using 6-hourly track data obtained from the South Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) database. A probabilistic clustering technique is applied to separate TC tracks into distinct groups in order to assess the primary cyclone trajectories for the region and its relationship with the El Niño-Southern Oscillation (ENSO). TC tracks are also classified into four sinuosity categories: straight, recurving, sinuous and highly sinuous; and their spatial and temporal characteristics subsequently analysed. The results of the cluster analysis identified five optimal groups of TC tracks, four of which exhibited southeast propagation, except for the southwest moving tracks in Cluster 5. Temporally, significant trends were observed over the last seven decades, with Clusters 1, 3 and 4 becoming less frequent with a substantial increase in the occurrence of Cluster 2 tracks (representing TCs east of dateline), a geometry favoured by El Niño conditions. Further, the sinuosity analysis revealed continued dominance of straight TCs within the eastern SWP with a tendency of encountering TCs of other morphology types. Conversely, the western SWP region is typically exposed to highly sinuous tracks. We also observed a significant decrease (increase) in TCs with straight and quasi-straight (highly sinuous) tracks, particularly during the last decade. These findings suggest that combined cluster analysis and TC track sinuosity analysis is an important tool in generalising the TC track regimes, refining predicted trajectories and understanding impacts on SWP island nations.

Tropical cyclones (TCs) represent a significant hazard to the southwest Pacific (SWP) region, impacting on properties, lives and infrastructure, accounting for ~76% of reported disasters within the region. A particular challenge that island nations face is the inherent degree of variability in TC risk from season to season, which hampers adaptation planning due to the difficulty in predicting how many TCs will form and the subsequent areas of impact. Therefore, this study aims to assess the historical variability of TC genesis and decay (i.e., the start and end of a TC life cycle) for the SWP over the last 70 years. This is achieved through a spatio‐temporal analysis of TC Best Track Data from South Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) dataset from 1948 to 2017 for TCs that originate within 0°–35°S and 135°E–120°W. Results highlight substantial decadal variability in dominant regions of genesis and decay over the last seven decades. In particular, we observe a statistically significant displacement of TC genesis (decay) by 898 km (909 km) in an east‐northeast (east‐southeast) direction from 1948 to 2017. We also demonstrate that TCs undergoing extratropical transition have significantly decreased in terms of both frequency and duration during the last four decades, however, the length of the extratropical cyclone tracks has increased. We attribute these observations to conducive environmental conditions, including warmer sea surface temperatures in the eastern region of TC genesis, sufficient moisture content (relative humidity) and favourable vertical wind shear. Further, the observed ocean warming and decreased wind shear during recent decades across the south of the SWP region favour the east‐southeasterly extension of extratropical cyclones. 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.

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