We will be visiting Chiang Mai from 01 October what is the whether like at the moment?

Hot - I should have added 12:42 in the afternoon 33C and sunny. My weather gadget says: 33-34C and intermittent thunder storms for the week.

Heat not a problem as we live in Hua Hin; more worried about rain curtailing things.

Really looks like the rainy season is fading, and that for September. So it looks good for October this year. During some years, heavy/prolonged rain persists until well into October, but it doesnt' look like it currently.

Look at the weather map; the key thing is the tropical storms near the Philippines; in a very rainy period those move due West and hit Vietnam and then (after losing some strength) Thailand. That's not happening now, the thing moves North, very slowly.

http://www.gophoto.it/view.php?i=http://www.tmd.go.th/programs\uploads\maps\2012-09-23_TopChart_07.jpg#.UF69lI3iZhs

Then later in October the high pressure over China expands and then significantly cooler weather kicks off. But it'll still be hot when you get here.

thank you, all looks good for our visit.