If you’re hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in Mersing: The hottest months are usually May and June, with an average temperature of 28°C, while the coldest months are January and February, with an average of 26°C. The rainiest months in Mersing are December, November, January and October, with each month seeing an average of 392 mm of rainfall.