Thais and Westerners alike often joke about the climate in Thailand. There are three distinct seasons in Thailand, so the joke goes, hot, hotter and hottest. The Hot Season begins in November and lasts through February. The Hotter Season begins in June and lasts through October while the Hottest Season comes between March and May with the hottest month usually April. Actually there really are only two distinct seasons: dry and wet. June, the time of our planned visit, is the starting of the wet season.
The best time to visit Thailand, most tour books will tell you, is during December and January. June, however, offers a great time to visit with daily rain showers which often cool the late afternoon sun and also, as an added benefit, dissipate the smog found throughout Bangkok. June average rainfall in Bangkok is 6.7 inches. June should be OK in Bangkok. I am not going to lie to you, it will be hot, very hot! Don't be surprise if you have trouble breathing when you first leave the airport.
So what should you bring to wear in Bangkok? Light, loose cotton clothing is best. Nylon and other synthetics should be avoided. Jackets and ties are required in a few restaurants and nightclubs. I don’t plan to go to such places but you may want to. Neat clothes (no shorts or tank tops) are required for entering temples or palaces. Shorts are OK for tourists but are not generally seen on adult Thais. It will be very hot so shorts may be OK depending on where we go. You are a tourist (kind of) and you may as well be comfortable and look like a “dumb” tourist. Again, Thai adults generally do not wear shorts, especially the men.
