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 Denman Island: The hottest months are usually August and July, with an average temperature of 16°C, while the coldest months are February and December, with an average of 4°C. The rainiest months in Denman Island are November, January, December and October, with each month seeing an average of 258 mm of rainfall.