Xiamen weather(https://www.travelchinaguide.com/climate/xiamen.htm) is mild and pleasant most of the year because the city has a subtropical monsoon climate.In this case, the whole year round is good time to visit Xiamen except that typhoons influence the weather four to five times during the months from July to September. March and April are good time to visit Xiamen with an gentle temperature of about 16~27C. You can wear some cloths, better prepare a light jacket in case cool at night.