Weather is probably a major factor when you plan your trip to Bioko Island, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually March and April with an average temp of 81°F, while the coldest months are August and July with an average of 77°F. The rainiest months in Bioko Island are August, June, July, and September, with each month seeing an average of 30 inches of rainfall.