Other facts from our historical weather data: Which months have the greatest rainfall in Siem Reap? Most rainfall (rainy season) is seen in May, June, July, August, September and October. Does Siem Reap have a dry season? Yes, the months of January, February and December are very dry. Which is the hottest month in Siem Reap? April has an average maximum temperature of 36°C (97°F) and is the hottest month of the year. Which is the coolest month in Siem Reap? The coolest month is December with an average maximum temperature of 32°C (90°F). Which is the wettest month in Siem Reap? September tops the wettest month list with 286mm (11.3 in) of rainfall. Which is the driest month in Siem Reap? January is the driest month with 10mm (0.4 in) of precipitation. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.