If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Nasu: The hottest months are usually August and July with an average temp of 69°F, while the coldest months are February and January with an average of 33°F. The rainiest months in Nasu are July, September, August, and June, with each month seeing an average of 10 inches of rainfall.