There is a great variety in Chiang Mai seasonal weather from cool, hot to rainy. Rainy season in Chiang Mai makes everything beautiful. The maximum temperature stay over 30° C in this season, evenings can be cool or hot depends if it is raining or not. Bad weather generally comes in 3 to 4 day periods, and alternates with excellent weather. So, some fortunate people can spend most of their time under the sun while others will enjoy rain, rain and more rain...
Chiang Mai weather averages show that rainy season is a bit of a lottery. Rain comes at anytime, day and night and in every form: heavy downpour or small drizzle. The landscape returns to its strikingly beautiful shade of green. Rainfall is generally heaviest in September. It would be better if you bring your stuff; otherwise, you will find plastic ponchos here.
