Palenque is in one of the wettest parts of Mexico. The rainy season runs from May to October, and in July and August the rainfall can be intense — the jungle around the ruins turns an almost artificial shade of green, and the waterfalls at Misol-Há and Agua Azul run at their fullest. The ruins are open rain or shine, and visiting in a light drizzle, with mist rising from the jungle, is atmospheric if damp.
The dry season from November to April is more comfortable for walking the ruins. December through February sees the most visitors, though the site never gets as crowded as Chichen Itza. Temperatures are warm year-round — the lowland heat in the dry season can be intense by midday. Early morning visits, which also mean fewer people and better light, are wise any time of year.