If the forecast is looking grim, why not head to Xiamen Museum? You'll be surprised just how much you can learn about the past here.
You'll have sightseeing choices galore in Siming District. Xiamen Museum is an ideal place to kick off here, but there are lots of other worthwhile sights to explore. Wanshi Botanical Garden, Xiamen University, and Nanputuo Temple are not far from the collection of historical artifacts and will round out your day nicely.