Click on a day for an hourly weather forecast
The temperatures in Karuizawa in September are comfortable with low of 12°C and and high up to 21°C.
You can expect about 3 to 8 days of rain in Karuizawa during the month of September. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.
Our weather forecast can give you a great sense of what weather to expect in Karuizawa in September 2025.
If you’re planning to visit Karuizawa in the near future, we highly recommend that you review the 14 day weather forecast for Karuizawa before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | -3° / -9° | 10 | 1 | 27 | 126 mm | Awful | Karuizawa in January |
| February | -1° / -9° | 10 | 1 | 22 | 106 mm | Awful | Karuizawa in February |
| March | 3° / -4° | 12 | 5 | 15 | 161 mm | Awful | Karuizawa in March |
| April | 11° / 1° | 9 | 19 | 3 | 153 mm | Awful | Karuizawa in April |
| May | 18° / 7° | 7 | 24 | 0 | 138 mm | Ok | Karuizawa in May |
| June | 22° / 11° | 8 | 22 | 0 | 166 mm | Ok | Karuizawa in June |
| July | 26° / 16° | 12 | 19 | 0 | 263 mm | Good | Karuizawa in July |
| August | 26° / 16° | 10 | 21 | 0 | 241 mm | Good | Karuizawa in August |
| September | 21° / 12° | 7 | 23 | 0 | 181 mm | Ok | Karuizawa in September |
| October | 14° / 6° | 6 | 25 | 0 | 200 mm | Good | Karuizawa in October |
| November | 8° / 1° | 8 | 17 | 5 | 120 mm | Awful | Karuizawa in November |
| December | 0° / -5° | 11 | 2 | 20 | 145 mm | Awful | Karuizawa in December |