SeasonMapKaruizawa weather in September
Japan
September in Karuizawa: nice, soaked, with clean air — fine if you can take 21 rainy days.
#2 of 12 months in Karuizawa · #750 of 1383 destinations to visit in September · comfort 78/100 (tier B)
Updated September 2026 · climate normals from ERA5 reanalysis
Traveller notes on Karuizawa in September
Other months in Karuizawa
Karuizawa's forum calls May one of the most pleasant months — its elevation keeps it noticeably cooler than Tokyo, with a day-to-night temperature swing of around 10°C that catches some visitors out. Regulars recommend layers for exactly that reason, plus a rain jacket just in case, and flag the first week of May (Golden Week) as considerably busier than the rest of the month.
Add your own note from Karuizawa's card on the map.
Karuizawa climate normals — September
| Daytime high | 21°C / 70°F | 😎 nice |
|---|---|---|
| Nighttime low | 13°C / 55°F | |
| Feels like (high) | 23°C / 73°F | |
| Rainfall | 179 mm / 7 in | ⛈ soaked |
| Rainy days | 21 days | |
| Humidity | 87% | 💦 very humid |
| Dew point | 16°C / 60°F | |
| Sunshine | 8 h/day | |
| Daylight | 12.4 h | |
| Wind | 8 km/h / 5 mph | |
| Air quality (US AQI) | 40 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Crowds in Karuizawa in September
How busy the place itself is — school and mass holidays, the months an editor tagged, and how sought-after the weather makes them. Never part of the comfort score.
Busyschool holidays in 3 of the markets that fill it, one of its best months for weather(estimated)
Peak crowdsBusyShoulder seasonQuiet
Best months for Karuizawa's weather
Ranked by this destination's own climate comfort score across the year — a different thing from how busy it gets (see Crowds above).
Best weatherKaruizawa's best weather comes in May, June and September — separate windows, not one continuous season.
Best weatherFair weatherToughest weather
Nearby, and something's on
Within 300 km of Karuizawa — a day trip or a short hop — with something on this month. Never part of the comfort score.
Where is Karuizawa?
Karuizawa in September — FAQ
- Is September a good time to visit Karuizawa?
- September in Karuizawa: nice, soaked, with clean air — fine if you can take 21 rainy days. It ranks #2 of 12 months for Karuizawa on SeasonMap's comfort score (78/100).
- What is the weather like in Karuizawa in September?
- In September, Karuizawa averages a daily high of 20.9°C and a low of 13°C, with about 178.9 mm of rain over roughly 20.5 rainy days.
- What is the air quality in Karuizawa in September?
- Karuizawa has a mean US Air Quality Index of about 40 in September.
Other months in Karuizawa
Compare Karuizawa in September
Warmer or cooler than Karuizawa in September
Similar destinations in East Asia — September
Within 300 km: Matsumoto's Kamikochi open season around 17 Apr – 15 Nov, and Hakuba's High trails and huts open around 1 Jul – 15 Oct.