Extratropical transition in the Southwest Indian Ocean

Tropical cyclones (TCs) in the Southwest Indian Ocean (SWIO) historically have received less attention than TCs in other ocean basins. One possible reason for the comparatively few TC-related studies in the SWIO is that significant in situ data limitations have only been partially addressed since the beginning of the modern satellite era. The absence of significant landmasses poleward of 25°S that can be impacted by TCs undergoing extratropical transition (ET) is a possible second factor in the fewer available TC-related studies in the SWIO. The purpose of this presentation will be to present the results of a SWIO TC/ET climatology and to show case studies of various ET events that are representative of this climatology.

A SWIO climatological analysis is constructed for the TC seasons (defined to be July through June) for 1989-2009 using the RSMC La Reunion and JTWC best-track datasets. In addition, the ECMWF Interim gridded dataset is used to provide a synoptic overview of the individual events. An analysis of the seasonal and interannual patterns of SWIO TCs and ET events will be presented and the results will be compared to TC and ET climatologies from other ocean basins. The ECMWF Interim gridded dataset is also used to conduct representative case studies of ET events in the SWIO. A brief overview of these case studies will be presented to illustrate the two primary synoptic patterns commonly associated with ET events observed in the SWIO as well as the effect of these patterns on the post-ET evolution of the transitioning cyclones.