If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Osaki: The hottest months are usually August and July, with an average temperature of 21°C, while the coldest months are January and February, with an average of 2°C. The rainiest months in Osaki are July, August, September and October, with each month seeing an average of 199 mm of rainfall.