Central Thailand experiences the country’s three seasons in equal measure: hot from February to June, rainy from June to October and cool (relatively speaking) from October to January. The one constant is the humidity.
Because of altitude, it is cooler (sometimes genuinely cold) and wetter in Sangkhlaburi and surrounding national parks than in other areas. Ayuthaya and Lopburi sit in a wide-open plain that receives similar amounts of rain and heat as Bangkok.