Planning for the weather is a good way to make your trip to Oshima-gun Yamato-son relaxing and enjoyable, especially when you're splurging. The hottest months are usually August and July, with an average temperature of 27°C, while the coldest months are January and February, with an average of 16°C. The rainiest months in Oshima-gun Yamato-son are June, May, August and September, with each month seeing an average of 323 mm of rainfall.