Using a reduced-gravity model, this study explores the ocean’s response to wind forcing in the South-East Tropical Indian Ocean (SETIO) during the development phase (July-September) of positive phases of the Indian Ocean Dipole (IOD), using the years of 2009 and 2019 for comparison. Findings show that IOD variability is exclusively controlled by zonal equatorial wind anomalies. In the average situation, represented by the 2009 season, westerly equatorial winds create downwelling Kelvin waves that operate to suppress the Sumatran upwelling. In contrast, positive phases of the IOD, represented by the 2019 season, are characterized by easterly equatorial winds that reverse the equatorial influence, which leads to strong coastal upwelling off Sumatra’s southeast coast. In addition, findings show that the Sumatran upwelling involves the formation of a strong northwestward surface flow, the South-East Sumatra Current, that transports colder seawater into the region, which contributes to the IOD anomaly.