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 Appi Onsen: The hottest months are usually August and July, with an average temperature of 18°C, while the coldest months are January and February, with an average of -4°C. The rainiest months in Appi Onsen are July, August, September and October, with each month seeing an average of 240 mm of rainfall.