If you're looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Haikou: The hottest months are usually June and July, with an average temperature of 29°C, while the coldest months are January and February, with an average of 21°C. The rainiest months in Haikou are August, October, July and September, with each month seeing an average of 256 mm of rainfall.