If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Yamanashi: The hottest months are usually August and July with an average temp of 66°F, while the coldest months are January and February with an average of 32°F. The rainiest months in Yamanashi are July, September, October, and June, with each month seeing an average of 9 inches of rainfall.