My wife and I are planning to go to Bangkok and Ko Samui or one of the nearby islands in late May or early June. Has anyone been during this time? I've heard mixed things about how much the rains are likely to impact our trip. We're avoiding the Andaman coast because it sounds like it gets hit the hardest.
We spent 5 weeks in Thailand from early June to mid July a few years ago. We were mainly in Bangkok and Phuket with some trips around and in the Andaman Sea.
When we went there was a fairly typical amount of rain for a tropical place from early June to early July,...it would rain, then clear up, then rain again...nothing that would interrupt our plans.
The last two weeks of our time there though, it completely changed. It literally started raining one day and really didn't stop until we left. It was torrential, like nothing I've ever seen. We were still able to do what we wanted to do but we were just wet all the time! We just took on the mindset of "If the locals are still going about their business, then we can too!" There were a couple of times where driving was a bit scary as water and mud washed across the roads in some places, and the creek behind the house we were staying in came up to the back gate, and the swimming pool overflowed!
Koh Samui is going to be in a different climate zone though...just do your research and do what you are comfortable with. No one can really predict the weather but you can make a fairly educated guess based on typical patterns. That said, weather is becoming more extreme and they have had severe flooding there in recent years although I believe it was around the months of Sept., Oct., November...May/June is typically drier in Koh Samui.