Planning for the weather is a good way to make your trip to Haikou relaxing and enjoyable, especially when you’re splurging. The hottest months are usually June and July with an average temp of 84°F, while the coldest months are January and February with an average of 69°F. The rainiest months in Haikou are August, October, July, and September, with each month seeing an average of 10 inches of rainfall.