How's the Weather?
In the highlands around San Cristóbal de las Casas the weather is cool and comfortable throughout the year—the average high is 20°C (68°F). Bring a sweater or jacket for the evening, as temperatures can fall drastically after the sun sets. (Men in San Juan Chamula wear woolly black cloaks to ward off the cold.) September is the peak of the rainy season, which officially starts in August and can run until early October. In the coastal lowlands, including Palenque and Villahermosa, it is always hot and humid. Temperatures peak in May and June at about 31°C (88°F). The sun is extremely strong, so make sure to bring a hat and plenty of sunblock.
Thanks to the warm weather and spectacular landscape, restaurants, cafés, and even hotel lobbies are often outdoors; if not, the doors and windows are wide open. Therefore, a comfortable and casual style reigns at most establishments, and the only rule to live by is long pants—and maybe even some repellent—for evening outings, to help protect you from hungry insects.