January Weather in Seiyo, Japan

Last updated: August 23, 2025

In January, the average temperature in Seiyo, Japan hovers around 4°C (40°F). Expect cool conditions, with nighttime lows dropping to a brisk -7°C (20°F) and daytime highs peaking at a mild 16°C (60°F). Be prepared for some wet days, as 60 mm (2.4 in) of precipitation can fall over 9 days, contributing to an average humidity level of 74%.

January Temperature in Seiyo

In January in Seiyo, the average temperature is 4°C (40°F). Maximums can reach 16°C (60°F), while minimums can drop to as low as -7°C (20°F). This diverse temperature range makes it essential for travelers to pack accordingly, including both warm layers and lighter clothing.

January Weather in Seiyo: Daily Temperature Highs, Lows, and Averages

The chart illustrates January temperature patterns in Seiyo, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Seiyo, January typically has an average temperature of 4°C (40°F), with highs reaching up to 16°C (60°F) and lows dropping to around -7°C (20°F).

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

January Precipitation in Seiyo

In Seiyo in January, the total precipitation amount is 60 mm (2.4 in), occurring over a span of 9 days.

January Precipitation Trends in Seiyo

The chart displays monthly precipitation patterns in Seiyo, with values for each month alongside January’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how January’s conditions compare to those of other months. In Seiyo, January typically receives around 60 mm (2.4 inches) of precipitation spread over approximately 9 days.

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

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Millimeters (mm) Inches (in)

January Humidity in Seiyo

In Seiyo in January humidity is 74%. With an average temperature of 4°C (40°F), this humidity feels like a chilly embrace that makes every breath a little heavier, which can be quite uncomfortable for traveling.

January Average Humidity in Seiyo

This chart illustrates the average monthly humidity levels in Seiyo, with January’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In January, average humidity in Seiyo is approximately 74%, offering insight into how humid the weather typically is during this month.

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

January UV Index in Seiyo

In Seiyo in January, the maximum UV index reaches 4, which corresponds to a moderate Exposure Category. With a time to burn of 30 minutes, it’s important to take precautions to protect your skin. You can find more details in the Hourly UV Index in Seiyo for better planning.

Maximum UV Index Levels in Seiyo for January

The chart shows the monthly maximum UV Index (UVI) for Seiyo in January, 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 January, the maximum UV index in Seiyo typically reaches 4, which falls under the moderate exposure category.

Data source: Seiyo January 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 January Weather in Seiyo Compares to Other Months

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

This table compares monthly weather conditions in Seiyo, showing how January’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	4°C (40°F)	60 mm (2.4 inches)	74%	moderate
February Weather	5°C (41°F)	97 mm (3.8 inches)	70%	high
March Weather	9°C (49°F)	140 mm (5.5 inches)	70%	very high
April Weather	14°C (57°F)	140 mm (5.5 inches)	76%	very high
May Weather	18°C (65°F)	174 mm (6.8 inches)	82%	extreme
June Weather	22°C (71°F)	236 mm (9.3 inches)	86%	extreme
July Weather	25°C (78°F)	409 mm (16.1 inches)	91%	extreme
August Weather	27°C (80°F)	219 mm (8.6 inches)	88%	extreme
September Weather	23°C (74°F)	229 mm (9.0 inches)	85%	extreme
October Weather	18°C (64°F)	213 mm (8.4 inches)	82%	very high
November Weather	11°C (52°F)	62 mm (2.4 inches)	79%	high
December Weather	6°C (43°F)	69 mm (2.7 inches)	77%	moderate