September Weather in Kosai, Japan

Last updated: August 23, 2025

In September, the average temperature in Kosai, Japan hovers around 25°C (78°F), creating a pleasant atmosphere for visitors. Expect minimums of 15°C (59°F) and maximums reaching 35°C (95°F), offering a range of experiences throughout the day. However, be prepared for 217 mm (8.5 in) of precipitation over 18 days, contributing to an average humidity of 87%. This unique climate makes Kosai an intriguing destination during this time of year!

September Temperature in Kosai

In September in Kosai, the average temperature is 25°C (78°F). Maximums can reach 35°C (95°F) and minimums can be as low as 15°C (59°F). This makes it an ideal time for travelers looking to enjoy warm weather while still having cooler evenings.

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

The chart illustrates September temperature patterns in Kosai, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Kosai, September typically has an average temperature of 25°C (78°F), with highs reaching up to 35°C (95°F) and lows dropping to around 15°C (59°F).

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

September Precipitation in Kosai

In Kosai in September, the total precipitation amount is 217 mm (8.5 in) spread over 18 days.

September Precipitation Trends in Kosai

The chart displays monthly precipitation patterns in Kosai, 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 Kosai, September typically receives around 217 mm (8.5 inches) of precipitation spread over approximately 18 days.

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

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Millimeters (mm) Inches (in)

September Humidity in Kosai

In Kosai in September, humidity is 87%. With an average temperature of 25°C (78°F), this humidity feels like a warm, heavy blanket enveloping you, making outdoor activities particularly strenuous and requiring frequent breaks for hydration and shade.

September Average Humidity in Kosai

This chart illustrates the average monthly humidity levels in Kosai, 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 Kosai is approximately 87%, 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 Kosai

In Kosai in September, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Kosai.

Maximum UV Index Levels in Kosai for September

The chart shows the monthly maximum UV Index (UVI) for Kosai 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 Kosai typically reaches 10, which falls under the very high exposure category.

Data source: Kosai 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 Kosai Compares to Other Months

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

This table compares monthly weather conditions in Kosai, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	6°C (44°F)	49 mm (1.9 inches)	82%	moderate
February Weather	7°C (45°F)	69 mm (2.7 inches)	79%	moderate
March Weather	12°C (53°F)	154 mm (6.1 inches)	74%	very high
April Weather	16°C (60°F)	160 mm (6.3 inches)	76%	very high
May Weather	20°C (69°F)	187 mm (7.4 inches)	83%	extreme
June Weather	23°C (74°F)	240 mm (9.4 inches)	87%	extreme
July Weather	27°C (81°F)	385 mm (15.2 inches)	93%	extreme
August Weather	29°C (85°F)	189 mm (7.4 inches)	91%	extreme
September Weather	25°C (78°F)	217 mm (8.5 inches)	87%	very high
October Weather	20°C (68°F)	284 mm (11.2 inches)	85%	high
November Weather	14°C (58°F)	75 mm (2.9 inches)	83%	moderate
December Weather	9°C (48°F)	65 mm (2.6 inches)	83%	moderate