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September Weather in Belfast, United States

Last updated: June 24, 2025

In September, the average temperature in Belfast, United States hovers around 16°C (62°F). However, temperatures can range significantly, dipping to a chilly 0°C (32°F) and peaking at a warm 31°C (88°F). Travelers should prepare for some wet days, as 77 mm (3.0 in) of precipitation is expected over 9 days, with an average humidity level of 76%.

September Temperature in Belfast

In September in Belfast, the average temperature is 16°C (62°F). Maximums can reach 31°C (88°F), while minimums can drop as low as 0°C (32°F). Be prepared for a variety of weather conditions when traveling during this time.

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

The chart illustrates September temperature patterns in Belfast, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Belfast, September typically has an average temperature of 16°C (62°F), with highs reaching up to 31°C (88°F) and lows dropping to around 0°C (32°F).
JanFebMarAprMayJunJulAugSepOctNovDec242734445665706862513730
Data source: Temperature data for Belfast 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 Belfast

In Belfast in September, the precipitation amount is 77 mm (3.0 in) over the course of 9 days.

September Precipitation Trends in Belfast

The chart displays monthly precipitation patterns in Belfast, 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 Belfast, September typically receives around 77 mm (3.0 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec7890801091179911884771278587
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Belfast

In Belfast in September, humidity is 76%. With an average temperature of 16°C (62°F), this humidity feels like a warm, enveloping blanket that makes exploring the outdoors feel both refreshing and slightly muggy, urging travelers to take breaks often and enjoy the shade.

September Average Humidity in Belfast

This chart illustrates the average monthly humidity levels in Belfast, 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 Belfast is approximately 76%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec91%91%88%88%82%80%77%72%76%83%88%87%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Belfast

In Belfast in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Belfast.

Maximum UV Index Levels in Belfast for September

The chart shows the monthly maximum UV Index (UVI) for Belfast 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 Belfast typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec356910101098642
Data source: Belfast 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 Belfast Compares to Other Months

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

This table compares monthly weather conditions in Belfast, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-4°C (24°F)78 mm (3.1 inches)91%moderate
February Weather-3°C (27°F)90 mm (3.5 inches)91%moderate
March Weather1°C (34°F)80 mm (3.1 inches)88%high
April Weather7°C (45°F)109 mm (4.3 inches)88%very high
May Weather14°C (57°F)117 mm (4.6 inches)82%very high
June Weather18°C (65°F)99 mm (3.9 inches)79%very high
July Weather21°C (70°F)118 mm (4.7 inches)77%very high
August Weather20°C (68°F)84 mm (3.3 inches)72%very high
September Weather16°C (62°F)77 mm (3.0 inches)76%very high
October Weather11°C (52°F)127 mm (5.0 inches)83%high
November Weather3°C (37°F)85 mm (3.4 inches)88%moderate
December Weather-1°C (30°F)87 mm (3.4 inches)87%low

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