Planning for the weather is a good way to make your trip to Ratchaburi relaxing and enjoyable, especially when you're splurging. 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.