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December Weather in Seiyo, Japan

Last updated: August 23, 2025

In Seiyo, Japan, the average temperature in December hovers around 6°C (43°F). Temperatures can dip as low as -3°C (28°F) and soar to a pleasant 21°C (70°F). Be prepared for some rain, with an average precipitation of 69 mm (2.7 in) spread across 8 days. With an average humidity of 77%, this month is sure to be an experience for the senses!

December Temperature in Seiyo

In December in Seiyo, the average temperature is 6°C (43°F). Maximum temperatures can reach 21°C (70°F), while the minimum can drop to as low as -3°C (28°F). Be prepared for a varied climate, offering a mix of cool and mild conditions perfect for exploring the outdoors.

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

The chart illustrates December 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, December typically has an average temperature of 6°C (43°F), with highs reaching up to 21°C (70°F) and lows dropping to around -3°C (28°F).
JanFebMarAprMayJunJulAugSepOctNovDec394149576571778073645243
Data source: Temperature data for Seiyo 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.

December Precipitation in Seiyo

In Seiyo in December, the precipitation amount is 69 mm (2.7 in) that falls over a period of 8 days.

December Precipitation Trends in Seiyo

The chart displays monthly precipitation patterns in Seiyo, with values for each month alongside December’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how December’s conditions compare to those of other months. In Seiyo, December typically receives around 69 mm (2.7 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec60971401401742364092192292136269
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Seiyo

In Seiyo in December humidity is 77%. With an average temperature of 6°C (43°F), this humidity feels like a damp chill that seeps into your bones, making it essential to dress warmly and stay active while exploring the area.

December Average Humidity in Seiyo

This chart illustrates the average monthly humidity levels in Seiyo, with December’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In December, average humidity in Seiyo is approximately 77%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec74%70%70%76%83%86%91%88%85%82%79%77%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in Seiyo

In Seiyo in December, 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 December

The chart shows the monthly maximum UV Index (UVI) for Seiyo in December, 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 December, the maximum UV index in Seiyo typically reaches 4, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec469101211121211864
Data source: Seiyo December 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 December 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 December’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 December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather4°C (40°F)60 mm (2.4 inches)74%moderate
February Weather5°C (41°F)97 mm (3.8 inches)70%high
March Weather9°C (49°F)140 mm (5.5 inches)70%very high
April Weather14°C (57°F)140 mm (5.5 inches)76%very high
May Weather18°C (65°F)174 mm (6.8 inches)82%extreme
June Weather22°C (71°F)236 mm (9.3 inches)86%extreme
July Weather25°C (78°F)409 mm (16.1 inches)91%extreme
August Weather27°C (80°F)219 mm (8.6 inches)88%extreme
September Weather23°C (74°F)229 mm (9.0 inches)85%extreme
October Weather18°C (64°F)213 mm (8.4 inches)82%very high
November Weather11°C (52°F)62 mm (2.4 inches)79%high
December Weather6°C (43°F)69 mm (2.7 inches)77%moderate

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