September Weather in Iwanai, Japan

Last updated: August 23, 2025

In September, the average temperature in Iwanai, Japan is a comfortable 18°C (64°F). Temperatures can vary significantly, with a minimum of 8°C (47°F) and soaring up to 28°C (82°F). Be prepared for some rain, as the region sees an average precipitation of 126 mm (5.0 in) over 15 days. With an average humidity of 88%, it's a typically moist period, so pack accordingly!

September Temperature in Iwanai

In September in Iwanai, the average temperature is 18°C (64°F). Maximums can reach 28°C (82°F), and minimums can drop to 8°C (47°F). This makes it a comfortable time to explore Iwanai, so pack layers for both warm and cooler moments during your travels.

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

The chart illustrates September temperature patterns in Iwanai, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Iwanai, September typically has an average temperature of 18°C (64°F), with highs reaching up to 28°C (82°F) and lows dropping to around 8°C (47°F).

Data source: Temperature data for Iwanai generated using information from the Copernicus Climate Change Service.

September Precipitation in Iwanai

In Iwanai in September, the precipitation amount is 126 mm (5.0 in) spread over 15 days.

September Precipitation Trends in Iwanai

The chart displays monthly precipitation patterns in Iwanai, 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 Iwanai, September typically receives around 126 mm (5.0 inches) of precipitation spread over approximately 15 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

September Humidity in Iwanai

In Iwanai in September, humidity is 88%. With an average temperature of 18°C (64°F), this humidity feels like you’re walking through a warm, enveloping mist, making every step slightly weighted but also refreshing, ideal for leisurely exploration but challenging for strenuous activities.

September Average Humidity in Iwanai

This chart illustrates the average monthly humidity levels in Iwanai, 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 Iwanai is approximately 88%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Iwanai

In Iwanai in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Iwanai.

Maximum UV Index Levels in Iwanai for September

The chart shows the monthly maximum UV Index (UVI) for Iwanai 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 Iwanai typically reaches 8, which falls under the very high exposure category.

Data source: Iwanai 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 Iwanai Compares to Other Months

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

This table compares monthly weather conditions in Iwanai, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	-4°C (25°F)	99 mm (3.9 inches)	84%	low
February Weather	-3°C (26°F)	103 mm (4.1 inches)	83%	moderate
March Weather	1°C (34°F)	98 mm (3.8 inches)	81%	moderate
April Weather	5°C (41°F)	88 mm (3.4 inches)	81%	high
May Weather	11°C (53°F)	86 mm (3.4 inches)	86%	very high
June Weather	15°C (59°F)	109 mm (4.3 inches)	87%	very high
July Weather	20°C (68°F)	94 mm (3.7 inches)	93%	very high
August Weather	21°C (70°F)	145 mm (5.7 inches)	95%	very high
September Weather	18°C (64°F)	126 mm (5.0 inches)	88%	very high
October Weather	12°C (53°F)	149 mm (5.9 inches)	83%	moderate
November Weather	5°C (41°F)	176 mm (6.9 inches)	79%	moderate
December Weather	-2°C (29°F)	159 mm (6.3 inches)	80%	low