Hi! Thailand is perfectly fine to visit in August. You'll find a few showers here and there but it's almost always sunny in the day! I went in August last year and only saw, maybe, two bouts of rain on the 10 day trip. Hope this helped!
August is a good time for Thailand. You will get god deals in august The summer months of April to May are preferred by foreigners but there are many people in tourist spots and things get expensive unlike the rainy months.