If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Mersing: The hottest months are usually May and June with an average temp of 82°F, while the coldest months are January and February with an average of 79°F. The rainiest months in Mersing are December, November, January, and October, with each month seeing an average of 15 inches of rainfall.