Other facts from our historical weather data: When is the rainy season in Ban Khao San? Rainy season in Ban Khao San occurs in the months of May, June, July, August and September. Does Ban Khao San have a dry season? Yes, the months of January, February and December are very dry. Which is the hottest month in Ban Khao San? April has an average maximum temperature of 37°C (99°F) and is the hottest month of the year. Which is the coolest month in Ban Khao San? The coolest month is January with an average maximum temperature of 30°C (86°F). Which is the wettest month in Ban Khao San? August tops the wettest month list with 317mm (12.5 in) of rainfall. Which is the driest month in Ban Khao San? December is the driest month with 7mm (0.3 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.