Thailand will officially enter the rainy season this Saturday, with more rain than last year and rainfall over the entire season anticipated to be 5%-10% more than average, says Meteorological Department Director-General Nattapon Nattasomboon.
Rainfall for the first half of the rainy season will be widespread and more than average but, in the second half, the situation will return to normal, he said, but warned of heavy rain, which may result in flash floods in some areas during the second half of the season.
The rainy season will end in October for the northern part of Thailand, but, in the southern region, especially on the eastern coast, the season will persist until January next year.
However the Royal Coast weather is typically very friendly as this previously published article explains. See https://royalcoastreview.com/2019/09/the-green-season-on-the-royal-coast-thailands-best-weather/