Two robust peaks in the diurnal evolution of orographically-locked precipitation are simulated in large-eddy simulations with an idealized ocean-plain-mountain topography. The ensemble experiment design is guided by sounding statistics from summertime afternoon thunderstorms in Taiwan to obtain realistic variability of free-tropospheric moisture associated with the intensity of the summertime subtropical high. The convection in the first peak is directly modulated by convective available potential energy, while the convection in the second peak is associated with low-level moist static energy (MSE) transport by the island-scale (40-km) local circulation, producing more extreme rainfall. When the initial free troposphere is drier, the convection in the second peak is strengthened. Both the environmental adjustments by the first peak and local circulation development contribute to the sensitivity of the second peak to free-tropospheric moisture. This work highlights the critical roles of convection-environment interaction and upstream MSE supply in enhancing extreme diurnal precipitation over complex topography.