Oaxaca City lies in a valley at an altitude of 5,000 feet. The city's easygoing personality is complemented by year-round spring temperatures, although days can get quite hot even in winter. Evenings can be chilly, so make sure to bring a light jacket.
Rainy season runs from July to October, September being the wettest month. Generally you can count on clear mornings, with clouds and showers usually arriving in the late afternoon.
The Oaxacan coast lies well within the tropics, so it's always hot and often humid.