If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Nanao: The hottest months are usually August and July with an average temp of 74°F, while the coldest months are February and January with an average of 41°F. The rainiest months in Nanao are July, September, August, and December, with each month seeing an average of 10 inches of rainfall.