Weather is probably a major factor when you plan your trip to Ratchaburi, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually April and May with an average temp of 86°F, while the coldest months are December and January with an average of 81°F. The rainiest months in Ratchaburi are September, October, May, and August, with each month seeing an average of 7 inches of rainfall.