CR 79:23-37 (2019)  -  DOI: https://doi.org/10.3354/cr01575

ABSTRACT: Common perception holds that tropical cyclones occur exclusively within the latitudinal range of 5° to 20°S. However, a few storms have been recorded poleward of this range each decade over the past half century. This study explores tropical cyclone occurrence south of the Tropic of Capricorn in the southwest Indian Ocean (SWIO; defined as 0°-30°S; African East coast up to 110°E). Using observational tropical cyclone and climate data, the small subset of storms making landfall in the region were examined in detail. The records indicate a decrease in storm frequency, while intensity has increased over the study period (1950-2015). Sea surface temperature (SST) reveals the interaction and influence of surface thermodynamics on tropical cyclone trajectory. Zonal wind at the 500 mb level indicates a modulation on track morphology following genesis, and may be responsible for recurving tracks. A decadal variability is observed for landfall location, which is currently in a low-amplitude southward component. SST is significantly related to storm intensity, while the Dipole Mean Index (DMI) and Southern Annular Mode (SAM) are related to and coincide with the highest landfall years. The Multivariate El Niño Southern Oscillation Index (MEI) is related to recurving track trajectories, while DMI and SAM may influence latitudinal and longitudinal track trajectories. These findings are important in understanding recent changes in tropical cyclone dynamics in the southwest Indian Ocean, particularly as the range of storm occurrence has expanded under climate warming.

KEY WORDS: Tropical cyclone · Southwest Indian Ocean · Tropic of Capricorn · Climatology · Climate Variability