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 temperature of 19°C, while the coldest months are January and February, with an average of 17°C. The rainiest months in Oaxaca are September, June, August and July, with each month seeing an average of 232 mm of rainfall.