The diurnal pattern of the July 2002 precipitation in the North American monsoon is simulated in a continuous one-month integration using the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model Version 5 (MM5) coupled with the Simplified Simple Biosphere (SSiB) land surface model. The simulation is conducted in a two-way, nested grid with a resolution of 45 km for the coarse domain and 15 km for the fine domain and only the fine domain that covers the core region of the North American monsoon is analyzed. Comparisons with the conventional gauge-based observations show that the coupled model successfully simulates the strength, position, and orientation of the monthly mean heavy rainbelt along the western slopes of Sierra Madre Occidental. In addition, the spatial pattern and phasing of the diurnal cycle of precipitation in this region agrees fairly well with the satellite observations from the Tropical Rainfall Measuring Mission (TRMM).