Planning for the weather is a good way to make your trip to Yonaguni relaxing and enjoyable, especially when you’re splurging. The hottest months are usually August and July with an average temp of 83°F, while the coldest months are January and February with an average of 68°F. The rainiest months in Yonaguni are May, August, September, and June, with each month seeing an average of 11 inches of rainfall.