If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Mishima: The hottest months are usually August and July with an average temp of 73°F, while the coldest months are January and February with an average of 44°F. The rainiest months in Mishima are June, July, September, and October, with each month seeing an average of 12 inches of rainfall.