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September Weather in Joetsu, Japan

Last updated: August 23, 2025

In September, the average temperature in Joetsu, Japan is a comfortable 23°C (74°F), with daytime highs reaching a sizzling 36°C (97°F) and lows dipping to a cool 14°C (57°F). Expect about 171 mm (6.7 in) of precipitation spread over 17 days, contributing to a notably high average humidity of 89%. Whether you're planning outdoor activities or seeking shelter from the rain, it's a month of diverse climate experiences!

September Temperature in Joetsu

In September in Joetsu, the average temperature is 23°C (74°F). The maximum can reach 36°C (97°F), while the minimum can be as low as 14°C (57°F). This makes it an ideal time to explore the region while enjoying warm days and mild evenings.

September Weather in Joetsu: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Joetsu, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Joetsu, September typically has an average temperature of 23°C (74°F), with highs reaching up to 36°C (97°F) and lows dropping to around 14°C (57°F).
JanFebMarAprMayJunJulAugSepOctNovDec383946536370788173645343
Data source: Temperature data for Joetsu generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Joetsu

In Joetsu in September, the precipitation amount is 171 mm (6.7 in) over the course of 17 days.

September Precipitation Trends in Joetsu

The chart displays monthly precipitation patterns in Joetsu, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Joetsu, September typically receives around 171 mm (6.7 inches) of precipitation spread over approximately 17 days.
JanFebMarAprMayJunJulAugSepOctNovDec233181128121105105290157171190170273
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Joetsu

In Joetsu in September humidity is 89%. With an average temperature of 23°C (74°F), this humidity feels like a warm, heavy blanket enveloping you, making traveling feel stifling and exhausting as you navigate the thick air.

September Average Humidity in Joetsu

This chart illustrates the average monthly humidity levels in Joetsu, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Joetsu is approximately 89%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec88%87%81%79%81%88%92%92%89%87%85%86%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Joetsu

In Joetsu in September, the maximum UV index is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check the Hourly UV Index in Joetsu.

Maximum UV Index Levels in Joetsu for September

The chart shows the monthly maximum UV Index (UVI) for Joetsu in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Joetsu typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3589101111119653
Data source: Joetsu September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Joetsu Compares to Other Months

Weather in Joetsu varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Joetsu, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Joetsu, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather3°C (38°F)233 mm (9.2 inches)88%moderate
February Weather4°C (39°F)181 mm (7.1 inches)86%moderate
March Weather8°C (46°F)128 mm (5.0 inches)81%very high
April Weather12°C (53°F)121 mm (4.7 inches)78%very high
May Weather17°C (64°F)105 mm (4.1 inches)81%very high
June Weather21°C (70°F)105 mm (4.1 inches)88%extreme
July Weather26°C (79°F)290 mm (11.4 inches)92%extreme
August Weather27°C (82°F)157 mm (6.2 inches)92%extreme
September Weather23°C (74°F)171 mm (6.7 inches)89%very high
October Weather18°C (64°F)190 mm (7.5 inches)87%high
November Weather12°C (53°F)170 mm (6.7 inches)85%moderate
December Weather6°C (43°F)273 mm (10.7 inches)86%moderate

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