November is the start of the high season, one reason is that it's dryer and cooler. But as others have pointed out, everything is relative - it will still be extremely warm and for some humid. I do recall last year, end of Nov where it was actually unbelievably pleasant, one week of almost no humidity.

You should dress for a warm summer weather (as opposed to hot humid), and bring a sweater for A/C hotel room and restaurants. Also, you will find wide variation of dress by visitors/tourists - but there is a certain decorum expected and maintained when visiting temples, shrines, etc.