An anomalous climate event occurred in 1997 in the Indian Ocean with severe consequences for the surrounding continental areas. In response to an intensification of the trade winds, a westward gradient of SST and an anomalous reversal of the eastward surface currents with peak velocity anomalies exceeding 1 m/s were evident in boreal autumn. A similar but weaker event took place in 1994. In this study we examine the observational record during the 1990s including surface drifter velocities, SST and altimeter sea level to confirm these dramatic changes. We examine the key momentum balance between wind-induced momentum flux and the pressure gradient force as well as the important role of horizontal temperature advection in the mixed layer heat response. ¿ 2001 American Geophysical Union