If you’re hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in Ratchaburi: The hottest months are usually April and May, with an average temperature of 30°C, while the coldest months are December and January, with an average of 27°C. The rainiest months in Ratchaburi are September, October, May and August, with each month seeing an average of 185 mm of rainfall.