Just thought I'd start this to keep anyone coming here over the next 3 months up to date with how the weather has been.
If you check forecasts for Koh Chang you'll see they pretty much all show a symbol that is a combination of thunderstorm, sunshine and rain and a 50% chance of rain, meaning pretty much anything could happen on any day and that doesn't help much.
There haven't been any really awful days so far although there have been a few days with torrential rain but limited to a few hours only. And there have even been some rather nice days.
The pattern recently has been pretty heavy rain very early morning which clears up after breakfast - around 10am. Then the sun comes out and the afternoons and evenings are, on the whole, pretty good. Or bright sunshine at sunrise and then it clouds over with a couple of hours rain and then the sun reappears again.
There are also isolated heavy showers on some days but these dont last too long, the clouds come in, the rain comes down, and 20 minutes later it clears up again.
Right now the sun is shining and the sea is pretty calm, safe for swimming.