Cambodia's wet season comes courtesy of the southwest monsoon which blows from May to October, bringing with it some 75% of Cambodia's annual rainfall. Not surprisingly, wet season is characterised by rain, and in the peak of wet season from July to September it can rain as much as two out of every three days. Rainy days tend to have a few hours of heavy rain rather than all-day downpours, though the latter do occur -- you will get wet travelling in a Cambodian wet season.