im heading off RTW at the end of sept beginning of oct and our first stop is thailand but i just found out that october is the beginning of the monsoon season. we were planning on heading south around ko samui will this be a complete washout at that time of year?
You will get rain at that time of year - not all day every day, but expect at least a few hours of rain most days - and obviously more overcast than otherwise.
It's not too bad then anyway - less people and the prices all come down too.
Hope that helps
If I'm not mistaken I heard a local say that on the gulf coast(east) they don't get mooson so bad as on the andaman sea coast (west), so Samui might not be so bad after all - but samui is not thailand, it is turist land, even if it won't be so packed as on other times of the year it is simply too developed...
Anyhow, have a good trip.