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September Weather in Castleknock, Ireland

Last updated: August 23, 2025

In Castleknock, Ireland, the average temperature in September hovers around 13°C (56°F). Expect a minimum of 3°C (38°F) and a pleasant maximum of 22°C (72°F). With average precipitation at 73 mm (2.9 in) spread over 14 days, expect some wet days. Additionally, the average humidity sits at a notable 86%, adding to the overall atmospheric feel of the month.

September Temperature in Castleknock

In September, in Castleknock, the average temperature is 13°C (56°F). Maximum temperatures can reach 22°C (72°F), while minimums can dip as low as 3°C (38°F). This mild climate makes Castleknock an ideal destination for travelers looking to enjoy comfortable outdoor activities.

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

The chart illustrates September temperature patterns in Castleknock, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Castleknock, September typically has an average temperature of 13°C (56°F), with highs reaching up to 22°C (72°F) and lows dropping to around 3°C (38°F).
JanFebMarAprMayJunJulAugSepOctNovDec424344475257605956514643
Data source: Temperature data for Castleknock 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 Castleknock

In Castleknock in September, the total precipitation amount is 73 mm (2.9 in) over the course of 14 days.

September Precipitation Trends in Castleknock

The chart displays monthly precipitation patterns in Castleknock, 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 Castleknock, September typically receives around 73 mm (2.9 inches) of precipitation spread over approximately 14 days.
JanFebMarAprMayJunJulAugSepOctNovDec578081527275809573879794
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Castleknock

In Castleknock in September, humidity is 86%. With an average temperature of 13°C (56°F), this humidity feels like a damp blanket enveloping you, making outdoor activities slightly uncomfortable and prompting travelers to seek shade or air-conditioned spaces frequently.

September Average Humidity in Castleknock

This chart illustrates the average monthly humidity levels in Castleknock, 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 Castleknock is approximately 86%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%86%86%85%83%85%86%85%86%87%87%84%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Castleknock

In Castleknock in September, the maximum UV index reaches 5, which corresponds to a moderate Exposure Category. Under these conditions, the estimated time to burn is approximately 30 minutes. For more details, you can check the Hourly UV Index in Castleknock.

Maximum UV Index Levels in Castleknock for September

The chart shows the monthly maximum UV Index (UVI) for Castleknock 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 Castleknock typically reaches 5, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec124578875321
Data source: Castleknock 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 Castleknock Compares to Other Months

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

This table compares monthly weather conditions in Castleknock, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather5°C (42°F)57 mm (2.2 inches)85%low
February Weather6°C (43°F)80 mm (3.1 inches)86%low
March Weather7°C (44°F)81 mm (3.2 inches)86%moderate
April Weather8°C (47°F)52 mm (2.0 inches)85%moderate
May Weather11°C (52°F)72 mm (2.8 inches)83%high
June Weather14°C (57°F)75 mm (3.0 inches)85%very high
July Weather16°C (60°F)80 mm (3.2 inches)86%very high
August Weather15°C (60°F)95 mm (3.8 inches)85%high
September Weather13°C (56°F)73 mm (2.9 inches)86%moderate
October Weather11°C (51°F)87 mm (3.4 inches)87%moderate
November Weather8°C (46°F)97 mm (3.8 inches)86%low
December Weather6°C (44°F)94 mm (3.7 inches)84%low

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