Weather is probably a major factor when you plan your trip to Wakura Onsen, and keep in mind that cheaper options are usually available when the weather isn't as good. 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 Wakura Onsen are July, September, August, and December, with each month seeing an average of 10 inches of rainfall.