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 Moriyama: The hottest months are usually August and July, with an average temperature of 24°C, while the coldest months are January and February, with an average of 5°C. The rainiest months in Moriyama are July, September, August and June, with each month seeing an average of 241 mm of rainfall.