Planning for the weather is a good way to make your trip to Tateyama relaxing and enjoyable, especially when you're splurging. 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 1°C. The rainiest months in Tateyama are July, December, September and August, with each month seeing an average of 299 mm of rainfall.