Using the combined infrared and microwave information from geostationary and TRMM satellites, the rainfall products of the PERSIANN (Precipitation Estimation from Remotely Sensed Information using Artificial Neural Network) system illustrate pronounced patterns of variability during the North American Monsoon. Over western Mexico, convection develops rapidly along the Sierra Madre Occidental from 1500-1700 LST (Local Sun Time) and persists until about local midnight. There is no convective rainfall detected over the nearby eastern Pacific Ocean western Baja peninsula; however, over extreme southern Mexico and northern Central America, intense convection forms over the land and then shifts offshore after local midnight (0000-0200 LST) off the southwestern coast of Mexico. This offshore convection grows in areal extent, appears to translate toward the southwest, and persists through midafternoon the next day. It is interesting to note that this daily cycle of convection moving offshore from southern Mexico appears to distort the ITCZ into a broad north-south zone of active convection extending westward to about 120oW. It is only this far-eastern Pacific Ocean region of the ITCZ that displays a very strong diurnal signal in the Boreal summer season. Results of mesoscale simulations using MM5 at 20 km x 20 km resolution reproduce many of these rainfall patterns detected in the PERSIANN analyses; however, the rainfall over tropics (south of 20° Latitude) is overestimated in comparison with PERSIANN and that over the subtropics is underestimated. Convective storms in the model simulations are triggered too early in the diurnal cycles and too frequently over the ITCZ and tropical regions, leading to the differences between the model results and the PERSIANN analyses.