The best time to visit Viñales is November through April, Cuba's dry season. The valley is green even then — the soil retains moisture well — but the humidity is lower, the nights are cool, and rain is rare. This is also the main tobacco harvest season, when the farms are most active and the drying sheds are full.
May through October brings the rainy season: heavy afternoon downpours are common, the mogotes disappear in cloud, and the valley roads can become muddy. Travel is still possible and the valley has its own atmosphere in the rain, but plan outdoor activities for the mornings. Hurricane season peaks September–October; Pinar del Río province is occasionally affected.