Wuzhishan's highland climate is considerably cooler and wetter than the coast, which is part of the point. November through April is the dry season and the best time for hiking; the mountain trail to Wuzhi peak is most reliably clear of cloud in December and January, when cold fronts from the north occasionally push the summit into sharp visibility.
The Yahu terraced fields are best seen in November when flooded or in September at harvest. The summer months — May through August — bring rain most days but the forest is lush and the heat is manageable compared to sea-level Hainan. July and August can be typhoon-adjacent, though the mountains provide some shelter from direct storm tracks.