Month 09 of 12
September
The heaviest month of the year on the central plains, and the one month where almost the whole country is wet at once.
In September, train in Koh Samui and Koh Phangan. Think twice about Bangkok, Pattaya and Hua Hin.
September is the peak of the wet stretch in Bangkok and Pattaya rather than merely a part of it. It is also the month the upper Gulf joins in, which puts Hua Hin into its own wet window, so the mainland, the Andaman coast and the upper Gulf are all wet simultaneously.
That leaves the southern Gulf as the last place standing, and it is the single most concentrated answer the calendar gives all year. If September is the only month available and the trip is about training rather than about Thailand, Samui or Phangan is where it goes.
8 regions
Inside the wet window
2 regions
Between the two
The month either side