Weather is probably a major factor when you plan your trip to Senami Onsen, but bear 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 temperature of 23°C, while the coldest months are February and January, with an average of 3°C. The rainiest months in Senami Onsen are July, December, January and August, with each month seeing an average of 257 mm of rainfall.