Thailand forum

Sep/Oct is the most unpredictably rainy times of the year, but that doesn't mean it rains all the time. You're slightly better off going to the lower gulf of Thailand (Ko Samui, etc) during July-August but Sep/Oct it's anyone's guess.

I'm a weather nerd - one place I'd avoid is the eastern Gulf in September. I can be okay but often real real wet.

I'd be looking maybe at the southern Gulf - it's wet season is normally Oct into Jan so late Sept may be okay. Samui is a possibility but you say quiet beach - I'd be looking at Had Yuan, Had Thian (east coast one) and Had Wai Nam on the east coast or Bottle Beach on the north coast or Had Mae on the west coast.

If you are super keen on Samui, google Thong Takien and Jungle Club.

Closer to Bangkok, Ko Samet which has the rep as the driest island in Thailand. Google Ao Pudsa/Ao Tubtim.
But of course, check what travelfish says abt all these places first.

Koh Maak is definitely smaller, quiet, and more laid back than Koh Samui, but the weather on Koh Maak could be a big issue that time of year and sandflies are a problem on many parts of the island. Plus, as much as I loved the time I spent on Koh Maak, I didn't think the beaches were as good as other places.

In addition to Koh Samui, Koh Samet as tezza suggests could be a good choice. It doesn't rain there as much as other places in the area, and there are several suitably romantic spots on the island. I'm not aware of a sandfly problem on Koh Samet, but it does get very crowded on the weekends, so you'd want to go mid week for the best experience.

If it were my call, that time of year and wanting a romantic spot, I'd go to Koh Samui. Hope that helps. Regards.

Strewth! Not too sure about all that color.