Planning for the weather is a good way to make your trip to Oaxaca relaxing and enjoyable, especially when you’re splurging. The hottest months are usually April and May with an average temp of 66°F, while the coldest months are January and February with an average of 62°F. The rainiest months in Oaxaca are September, June, August, and July, with each month seeing an average of 9 inches of rainfall.