The diurnal cycle of liquid water path (LWP) over the subtropical and tropical oceans is examined using two complete years of TMI (Tropical Rainfall Measuring Mission Microwave Imager) satellite microwave radiometer data. Diurnal amplitudes are a considerable fraction of the mean, especially in low cloud regions to the west of continents, where values of 15--35% are typical. Early morning maxima occur throughout most of the subtropics, consistent with a diurnal cycle driven largely by cloud solar absorption. In deep convective regions of the west Pacific the diurnal cycle is also strong and peaks slightly later. Interestingly, the diurnal amplitude in the SE Pacific and Atlantic stratus regions is considerably larger than in their northern hemisphere counterparts, suggesting differences in the dynamics and structure of low clouds may exist from region to region. The data provide important constraints for models simulating the diurnal cycle of clouds.