By August in Cambodia rainfall has peaked, river levels are high, Tonle Sap Lake is bountiful in fish and Angkor resplendently encircled by lotus filled moats.
Typical days are hot and humid with temperatures in the high twenties or low thirties. The humid air is cleared on most days by a short sudden late afternoon downpour or occasional thunderstorm.
Angkor receives far fewer visitors in these months, which for many really enhances the experience. Bear in mind at Angkor though that the temples are steep and the stones can be slippery when wet.
August is probably not the best time to head off into rural Cambodia where the infrastructure is poor and roads can become impassable.