Wenchang's northeast coastal position means it is one of the wetter parts of Hainan. The dry season runs from November through April, which is the best time for the Dongjiao peninsula and coastal exploration. May through September brings heavier rain and typhoon exposure — tropical storms track across the northeast coast more frequently than they affect the sheltered south.
The teahouse culture and the old town are enjoyable year-round regardless of weather, and the Confucius Temple district is particularly atmospheric in the cooler months. If your interest is in timing a visit to coincide with a rocket launch from the nearby Wenchang Space Center, launch schedules are announced on the China National Space Administration website with a few days' notice.