Karuizawa Weather in September
Thinking of visiting Karuizawa in September? Expect high temperatures reaching 24°C (75°F) during the day, dropping to 15°C (59°F) at night. Heavy showers are common during the rainy season.
Rainfall in Karuizawa in September
Karuizawa is in the rainy season in September, with rain on around 20 days and an average of 224 mm (8.8 in). With rain on many days and solid totals, showers are frequent and often moderately heavy. Waterproof gear is a sensible idea.
Temperature in Karuizawa in September
Daytime temperatures in Karuizawa reach 24°C (75°F) in September, dropping to 15°C (59°F) at night. The summer season is characteristic of September. Overall, the month follows a fairly predictable daily temperature pattern. At 15°C (59°F) overnight, it can feel quite a bit cooler after dark. Worth packing something warmer for evenings, but the cooler temperatures are ideal for sleeping.
Sunshine in Karuizawa in September
With about 142 hours of sunshine, the area enjoys a nice balance of sun and rainy moments, creating a pleasant environment.If you prefer dry days with pleasant temperatures, May typically offers the best circumstances. If you're seeking pleasant, dry and sunny weather somewhere else in the world, our weather planner can help you explore other options.
Check the conditions for any month of the year.
For a detailed overview over the year and the best time to visit Japan, check out our Karuizawa's climate page.
Karuizawa Temperature in September
Min Temperature
15°C (59°F)
Max Temperature
24°C (75°F)
Chance of Rain
66%
Precipitation
224 mm (8.8 in)
Rainy days
20 days
Humidity
74% *
Sunshine
142 hours *
Percentage Sunshine
*
Daily Historical Temperatures
50-year average (1976-2025)
Based on our historical records, temperatures in Karuizawa typically drop from around 26°C (79°F) at the start of September to approximately 20°C (68°F) by the end. Nights are pleasant, with lows typically ranging from 12°C (54°F) to 18°C (64°F).
Average temperatures in September
Daily Historical Precipitation
50-year average (1976-2025)
Average daily rainfall for each day of the month based on long-term records.
Average precipitation in September
Historical weather for Karuizawa in September
Browse day-by-day weather records for Karuizawa spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.
Karuizawa historical weather extremes in September
Based on 49 years of weather observations in Karuizawa between 1976 and 2025, these are the recorded extremes.
- Karuizawa recorded its highest September temperature of 35°C (95°F) on September 1, 2025.
- On September 30, 1996, Karuizawa saw its coldest September day with temperatures maxing out at 11°C (52°F).
- The lowest overnight temperature recorded in September was 3°C (37°F) (September 26, 2010).
Best Places in Japan in September
Find out more about the weather in Japan and which places have the best travel conditions in this month. See all of Japan in September →
perfect weather
pleasant
tolerable
unpleasant
poor
What to Wear in Karuizawa in September
For Karuizawa in September, you'll want flexible clothing. It's wise to pack cotton shirts, comfortable shorts, and a pair of jeans for cooler evenings. A light sweater or jacket is useful for air-conditioned spaces (like buses) or unexpected cool moments. Also bring a poncho, it will rain a lot! Waterproof everything you can. Bring sunglasses since you'll have some sunny periods throughout the monthWhat To Do in Karuizawa in September
We rated the following activities from 1 (least suitable) to 10 (best) to do.
Check the conditions for any month of the year.
For a detailed overview over the year and the best time to visit Japan, check out our Karuizawa's climate page.
Temperature Rainfall Sunshine Humidity
See the full Karuizawa climate overview or explore weather in Japan.
