For those suggesting that the weather in May-June is not that bad… keep in mind, everyone has their own ideas of what ‘not that bad’ is.
Make no mistake, divjan, it will be hot. For some, agreeable. For others, tolerable. And yet for others, downright intolerable. IMO, here’s what you can expect from a Chiang Mai perspective: Your day temps will easily reach the 90’s. May even reach 100. The humidity will also be stifling. You will be uncomfortable at times. After the sun sets, it will be quite comfortable (at least it was for me), but still pretty darned humid.

The afternoon thunderstorms will be likely and will only cool things down until the sun reappears. IMO, the thunderstorms are some of the most enjoyable things about Thailand. The cloudscapes and thunderheads are gorgeous.

In short, if you are a person who does not tolerate hot humid weather and rathers cool climates, you will most likely be uncomfortable at times. Me? Love the heat/humidity. Freakin’ love it.