If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Merritt Island: The hottest months are usually August and July with an average temp of 81°F, while the coldest months are January and February with an average of 66°F. The rainiest months in Merritt Island are September, August, July, and June, with each month seeing an average of 7 inches of rainfall.