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September Weather in Cornwall, Canada

Last updated: June 18, 2025

In Cornwall, Canada, the average temperature in September hovers around 16°C (62°F), creating a mild climate for visitors. However, temperatures can range from a chilly 0°C (32°F) to a warm 32°C (90°F), offering a variety of weather experiences. Be prepared for 70 mm (2.8 in) of precipitation over 9 days, and note the average humidity is a high 78%, ensuring a refreshing atmosphere throughout the month.

September Temperature in Cornwall

In September in Cornwall, the average temperature is 16°C (62°F). Maximums can reach 32°C (90°F), while minimums can drop as low as 0°C (32°F). Be prepared for a wide range of temperatures during your travels!

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

The chart illustrates September temperature patterns in Cornwall, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Cornwall, September typically has an average temperature of 16°C (62°F), with highs reaching up to 32°C (90°F) and lows dropping to around 0°C (32°F).
JanFebMarAprMayJunJulAugSepOctNovDec192230435766716962503626
Data source: Temperature data for Cornwall 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 Cornwall

In Cornwall in September, the total precipitation amount is 70 mm (2.8 in) spread over 9 days.

September Precipitation Trends in Cornwall

The chart displays monthly precipitation patterns in Cornwall, 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 Cornwall, September typically receives around 70 mm (2.8 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec8583871171091001161007013910884
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Cornwall

In Cornwall in September, humidity is 78%. With an average temperature of 16°C (62°F), this humidity feels like a warm blanket wrapping around you, making outdoor activities enjoyable yet slightly sticky. Travelers may find the weather pleasantly mild, though they'll appreciate having light, breathable clothing on hand to stay comfortable while exploring.

September Average Humidity in Cornwall

This chart illustrates the average monthly humidity levels in Cornwall, 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 Cornwall is approximately 78%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec93%92%86%85%80%74%76%75%78%86%89%89%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Cornwall

In Cornwall in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Cornwall.

Maximum UV Index Levels in Cornwall for September

The chart shows the monthly maximum UV Index (UVI) for Cornwall 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 Cornwall typically reaches 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec245899987532
Data source: Cornwall 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 Cornwall Compares to Other Months

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

This table compares monthly weather conditions in Cornwall, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-7°C (20°F)85 mm (3.3 inches)93%low
February Weather-6°C (22°F)83 mm (3.3 inches)92%moderate
March Weather-1°C (30°F)87 mm (3.4 inches)86%moderate
April Weather6°C (44°F)117 mm (4.6 inches)85%very high
May Weather14°C (57°F)109 mm (4.3 inches)80%very high
June Weather19°C (66°F)100 mm (3.9 inches)74%very high
July Weather22°C (72°F)116 mm (4.6 inches)76%very high
August Weather21°C (70°F)100 mm (3.9 inches)75%very high
September Weather16°C (62°F)70 mm (2.8 inches)78%high
October Weather10°C (51°F)139 mm (5.5 inches)86%moderate
November Weather2°C (36°F)108 mm (4.2 inches)88%moderate
December Weather-3°C (26°F)84 mm (3.3 inches)89%low

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