In recent years, India has been increasingly experiencing widespread flooding induced by large-scale extreme rainfall events (LEREs). These events are mainly associated with the monsoon low-pressure systems (LPSs) and occur mostly in their southwestern sector. The forecast of these high-flood-potential events, however, has remained challenging. In this study, we compare the LPSs of the Indian summer monsoon that lead to LEREs (LPS-Lg) and the strong LPSs that did not result in LEREs (LPS-noLg) over central India for the period 1979-2012. We show that having a strong LPS is not a sufficient condition to produce LEREs. Rather, an observed consistent feature is that the LPS-Lgs are accompanied by Secondary Cyclonic Vortices (SCVs). SCVs enhance dynamic lifting, static instability, and moisture transport from the Arabian Sea that precondition the atmosphere for deep convection. The simultaneous existence of an LPS and an SCV creates a giant mid-tropospheric vortex that helps in organizing the deep convection. SCVs also slow down the propagation of LPSs. We show that the interaction of multiple synoptic-scale systems can lead to LERE even if individual systems are not strong enough.