Weather is probably a major factor when you plan your trip to Chengmai, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually June and May, with an average temperature of 28°C, while the coldest months are January and December, with an average of 20°C. The rainiest months in Chengmai are August, July, September and May, with each month seeing an average of 264 mm of rainfall.