There is a good Hainan weather forecast website there.

Ocean tides, ocean tidal range, waves, temperature and salinity of high surface seawater and hydrological evaluation of surface seawater.

106 ~ 332cm67 ~136cm0.7 ~1.5m25.7 ~ 28.4℃ 25.6 ~ 33.2 ‰ Tropical marine characteristics in South China.

/service/Tianchi . htm

See if it's what you want.