We just came back from Sanya in Hainan island, and it was HOT.
According to http://chinasanya.com/cgi-bin/about/hainan.htm
"Climate
The Hainan Province climate is the tropical monsoon climate and the tropical oceanic climate. It's always high temperature and wet, dry and rainy seasons are distinct. There are more tropical storms and typhoon in summer. The average temperature very year is 22-26℃, in January-February average temperature is 16-24℃ and in July-August the average temperature is 25-29℃. It's like spring all the year round."