Weather will likely play an important role when you plan your trip to Beihai, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually July and August with an average temp of 84°F, while the coldest months are January and December with an average of 65°F. The rainiest months in Beihai are August, July, June, and September, with each month seeing an average of 15 inches of rainfall.