Developing a new sinuosity index for cyclone tracks in the tropical South Pacific

This paper introduces a new metric for tropical cyclone track shape within the tropical South Pacific (TSP) basin, based on measurements of track sinuosity. A sinuosity index (SI) is developed by applying a simple cube-root transformation to original track sinuosity values. Based on the resulting near-normal SI distribution, an ordinal four-category (quartile) naming system is then proposed for track-type classification. Track sinuosity patterns are also investigated over the last four decades (1970–2008). Analytical findings suggest that cyclone track sinuosity is an important parameter influencing the potential vulnerability of island archipelagoes to cyclone hazard. Principally, sinuously moving cyclones show some tendency for greater longevity and intensity than straighter-tracking storms and make up a larger proportion of systems forming in the western tropical South Pacific than those generated farther east. Although no long-term statistical trend can be established, track sinuosity is highly variable through time, implying that the TSP basin and the islands therein will continue to experience large but irregular inter-annual fluctuations in cyclone track morphology. Copyright Springer Science+Business Media B.V. 2011