The influence of ENSO on tropical cyclone trajectories in the South Indian Ocean

Hierarchical cluster analysis using the group average linkage method is performed on 192 South Indian Ocean (SIO) tropical cyclones (TCs) spanning the years 1979 to 2008 from the Joint Typhoon Warning Center best-track dataset. Four groups of TC trajectories are identified corresponding to strong and weak El Niņo events and strong and weak La Niņa events. Using a Kruskal-Wallis one-way analysis of variance on ranks test, the four clusters are then tested for differences in median trajectory bearings, speeds of forward motion, tortuosity, maximum lifetime intensity, latitude and longitude of initial and final fixes, track duration and distance. Preliminary results indicate that, similar to other ocean basins, TCs in the SIO tend to recurve and move farther eastward during strong warm events while following a more zonal track farther westward during strong cold events.