Climatic Determinants and Statistical Prediction of Tropical Cyclone Days in the Southwest Indian Ocean

Abstract

Abstract Climatic determinants of tropical cyclone (TC) days in the southwest Indian Ocean area (10°–25°S, 50°–70°E) are analyzed using statistical techniques. A TC days index is formulated from records of local meteorological services over the December–March season in the period 1961–91. The index is correlated with gridded fields of sea surface temperature (SST), outgoing longwave radiation (OLR), and tropospheric winds, using monthly standardized departures at various lags. SST relationships with TC days are positive over the entire southwest Indian Ocean from −4 to +2 months, as expected. Peak correlations of >+0.5 occur in the genesis region 0°–10°S, 50°–60°E to the northeast of Madagascar at lag −4 (September). The synoptic-scale response of monsoon convection is approximated by OLR correlations. Negative correlations (associated with increased convection) are found to the northeast of Madagascar at lag −4 and 0 months. At lags −4 and −2 (November) opposing positive OLR correlations are found over A...