Composite structure of tropical cyclones in the SW Indian Ocean

This work examines SW Indian Ocean tropical cyclone (TC) structure as a function of movement using ECMWF gridded data. Analyses of the mean summer climate for the period 1987­ 1992 shown that conditions conducive to the development ofTCs are present between the latitudes 5° and 15°S. Six westward moving TCs are selected to form the westward moving composite TC and four are used in the recurving TC composite from 3-days before the maximum surface intensity to 1­ day after. The westward moving composite was found to have a steady TC signature. Comparisons were made with TC Firinga which passed near Mauritius on 29 January 1989. The recurving TC composite was found to exhibit rapid growth with sharp parameters tendencies. Interaction with a sub­ tropical trough is seen in both TC composites. Upper level westerly winds create effective uplift which strengthens the recurving TC on the poleward side. Spectral analysis of a rainfall index compiled from Mauritius data demonstrates spectral peaks at the seasonal and intra-seasonal scale. Three peaks were identified. one within the 40-60 day Madden­ Julian Oscillation. one at 23 days and one with a 16 day oscillation. The 23 day oscillation was found to have a highest spectral power. The results of TC and rainfall analyses offer useful insights to the climate and weather of the SW Indian Ocean