Planning for the weather is a good way to make your trip to Tonami relaxing and enjoyable, especially when you’re splurging. The hottest months are usually August and July, with an average temperature of 23°C, while the coldest months are January and February, with an average of 3°C. The rainiest months in Tonami are July, September, December and August, with each month seeing an average of 250 mm of rainfall.