Weather will likely play an important role when you plan your trip to Tateyama, but bear in mind that cheaper options are usually available when the weather isn't as good. 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.