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September Weather in Harwell, United Kingdom

Last updated: August 27, 2025

In September, the average temperature in Harwell, United Kingdom hovers around 15°C (59°F). Expect a minimum of 2°C (37°F) and a pleasant maximum of 28°C (83°F). However, be prepared for some rain, as 50 mm (2.0 in) of precipitation is likely over 9 days. With an average humidity of 82%, it's wise to embrace the tropical vibe!

September Temperature in Harwell

In September in Harwell, the average temperature is 15°C (59°F). Maximum temperatures can reach 28°C (83°F), while the minimum can drop to as low as 2°C (37°F). This makes Harwell a great destination for travelers seeking mild weather, but it's wise to pack layers for varying conditions.

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

The chart illustrates September temperature patterns in Harwell, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Harwell, September typically has an average temperature of 15°C (59°F), with highs reaching up to 28°C (83°F) and lows dropping to around 2°C (37°F).
JanFebMarAprMayJunJulAugSepOctNovDec414345495461646358524643
Data source: Temperature data for Harwell 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 Harwell

In Harwell in September, the precipitation amount is 50 mm (2.0 in) over the course of 9 days.

September Precipitation Trends in Harwell

The chart displays monthly precipitation patterns in Harwell, 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 Harwell, September typically receives around 50 mm (2.0 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec505360386975637150975684
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Harwell

In Harwell in September, humidity is 82%. With an average temperature of 15°C (59°F), this humidity feels like a heavy blanket wrapping around you, making outdoor activities feel sticky and uncomfortable for travelers.

September Average Humidity in Harwell

This chart illustrates the average monthly humidity levels in Harwell, 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 Harwell is approximately 82%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec91%89%86%85%79%81%71%76%82%91%92%92%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Harwell

In Harwell in September, the maximum UV index is 6, which corresponds to a high Exposure Category. The time to burn is approximately 25 minutes. To find the hourly UV index in Harwell, you can refer to this Hourly UV Index in Harwell.

Maximum UV Index Levels in Harwell for September

The chart shows the monthly maximum UV Index (UVI) for Harwell 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 Harwell typically reaches 6, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec124678876421
Data source: Harwell 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 Harwell Compares to Other Months

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

This table compares monthly weather conditions in Harwell, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather5°C (41°F)50 mm (2.0 inches)91%low
February Weather6°C (43°F)53 mm (2.1 inches)89%low
March Weather7°C (45°F)59 mm (2.3 inches)86%moderate
April Weather9°C (49°F)38 mm (1.5 inches)85%high
May Weather12°C (55°F)69 mm (2.7 inches)79%high
June Weather16°C (61°F)75 mm (3.0 inches)80%very high
July Weather18°C (65°F)63 mm (2.5 inches)71%very high
August Weather17°C (63°F)71 mm (2.8 inches)76%high
September Weather15°C (59°F)50 mm (2.0 inches)82%high
October Weather11°C (53°F)97 mm (3.8 inches)90%moderate
November Weather8°C (46°F)56 mm (2.2 inches)92%low
December Weather6°C (43°F)84 mm (3.3 inches)92%low

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