The Rainy Season: July to October, average 28c
The post hot season rains do fall at this time but not continuously. Showers tend to be short bursts of heavy rain although these can bring inland flooding in central and northern Thailand, including Bangkok.
On the Gulf Coast however, the rain comes much later in October and November meaning July and August is a peak period to visit this coast with dry and sunny weather.
The heaviest coastal rains are on the Andaman coast between June and August which is the low season here and whilst Phuket functions year round, some of the smaller islands are inaccessible during this time.