Oaxaca enjoys a pleasant climate year-round. The warmest months are usually April and May, when daytime temps can reach into the 90s, but since it is a dry heat, it's invariably pleasant in the shade. The rainy season begins in late spring and continues through to early fall. You can expect rain in the afternoons during that time of year, but it's not a bad time to visit: dry, brown landscapes turn lush and green. The coolest months are December and January, when nights and mornings are decidedly chilly, but daytimes are warm and sunny.