Thailand forum

The southern Gulf islands (Samui, Phangan, Tao) are usually real good in August - still well short of their normal wet season of Oct into Jan. It does rain, but sunshine usually dominates.

Elsewhere is wet season, but travel is usually okay - we get plenty of posts saying people had a good holiday with the usual daily mixture of one or a few showers/storms and sunshine/scattered cloud, some days with no rain.
This has been the pattern in all my wet season visits. In August 07, I was on Phi Phi and Phuket in what the newspapers called the wettest period for some years. In 15 days got 2 days virtually cloudless, about 2 where it rained more often than not (but these still had some sunny breaks and were not write-offs), and the rest were the normal mixture of one or a few showers, sun/scattered cloud. I had a great holiday. In August 09 I spent 4 days on the Phuket side. One was real windy, mostly sunny, a few short showers - the others were not windy, otherwise similar. Check the uncredited shots on the 2 Phi Phi pages and 1 Phuket page in the link below, lots of sunshine in them. BTW, Phi Phi/Phuket and Krabi are within sight of each other, so weather patterns are similar.
This August I was on Samui and Phangan - I think it rained twice for all of 20 minutes in the 3 weeks.

The driest of the non-Southern Gulf islands tends to be Ko Samet near Bangkok. Most of Samet's beaches face east and are sheltered from the prevailing wet season winds which on the days when they get stronger can cause rough seas and blow a lot of flotsam and jetsom onto the beach.
The wettest are Big Ko Chang and neighbours + the Ranong area islands. Nevertheless I have seen plenty of posts from visitors to the former in the wet season saying they enjoyed themselves.

I hear ya walkingtrees. I'm originally from Seattle too but now live in Chiang Mai. I grew up hating rain but now I see it as a relief from the tropical heat. Don't worry too much about rain for your Thai trip in August - you will definitely get some on maybe half of your days but it seldom lasts all day and is often limited to brief thunderstorms which can be pretty impressive. By the end of your trip you may see rain in a different way. Carry a small collapsable umbrella (available for $3 everywhere) which also makes a good sunshade when you've had enough photons. As weathernerd Tezza indicates, the southern gulf coast and islands generally have the sunnier weather at this time and don't tend to get wet until around Oct/Nov.

Headed between Bangkok to Surat Thani, I have enjoyed going by day train and stopping off at less touristy places like Prachuap Khiri Khan, Bang Saphan, and Ban Krut. Also, Chumphon is a nice manageable town with good beaches out on the coast and way less western tourists than the popular islands. Happy planning.