Planning for the weather is a good way to make your trip to Nikko relaxing and enjoyable, especially when you’re splurging. The hottest months are usually August and July with an average temp of 70°F, while the coldest months are January and February with an average of 34°F. The rainiest months in Nikko are July, September, June, and August, with each month seeing an average of 10 inches of rainfall.