The country is quickly embracing the 21st Century and very accepting of tourists however it is still pretty conservative country with strong beliefs about modesty. So the suggestion is to think twice before packing your suitcases. The question isn't just: what's weather appropriate, but what's culturally appropriate. You are gonna visiting country which features numerous temples and is year-round warm.
Heat and humidity is through the country, therefore warm clothes are not needed.
We recommend you wear T-Shirt or blouse during visit to temples, pagodas or local family. Man can wear over-knee shorts while women should not wear short skirts.