In this study, cloud-resolving simulations are performed under idealized and uniform southwesterly flow direction and speed to investigate the rainfall regimes in the Mei-yu season and the role of complex mesoscale topography on rainfall without the influence of unwanted disturbances, including a low-Froude number regime where the thermodynamic effects and island circulation dominate, a high-Froude number regime where topographic rainfall in a flow-over scenario prevails, and a mixed regime.