September Weather in Belfast, United Kingdom

Last updated: March 17, 2025

September in Belfast, United Kingdom, offers a delightful blend of mild temperatures and occasional rainfall, making it a month of transition. Daily highs can reach up to 21°C (71°F), while the average temperature hovers around a comfortable 13°C (56°F). As the season changes, the nights can get quite cool, dipping to a minimum of 4°C (39°F). With 75 mm (3.0 in) of precipitation spread across 15 days, visitors should be prepared for sporadic showers. The high humidity level of 88% adds a unique touch to the crisp autumn air, creating an inviting atmosphere to explore the city's vibrant culture and scenic landscapes.

September Temperature in Belfast

As September unfolds in Belfast, United Kingdom, the city begins to transition from the warmth of summer to the cooler embrace of autumn. With temperatures ranging from a minimum of 4°C (39°F) to a pleasant maximum of 21°C (71°F), the month presents a comfortable average of 13°C (56°F). This gradual cooling trend indicates a delightful change, as the days still carry a hint of summer's warmth, while the evenings invite cozy layers. As the month progresses, the crispness in the air foreshadows the approach of October, making September a perfect time to enjoy Belfast’s rich autumnal beauty.

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.
JanFebMarAprMayJunJulAugSepOctNovDec424344475257605956514744
Data source: Temperature data for Belfast generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Belfast

In September, Belfast experiences a moderate precipitation level of 75 mm (3.0 in), occurring over 15 days, which signals a continuation of the wetter summer months. Following August’s peak of 115 mm, September marks a slight decrease, yet the rainfall remains significant, indicative of the city's typical transition into autumn. As the year progresses, rainfall in the subsequent months tends to rise again, with October and November both showcasing similar precipitation levels around 92 mm (3.6 in) and 94 mm (3.7 in), respectively. This pattern reflects a clear trend of increased rainfall as the seasons shift, contributing to Belfast's reputation for its damp climate.

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.
JanFebMarAprMayJunJulAugSepOctNovDec6089804566788411575929491
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Belfast

As September unfolds in Belfast, the city's humidity reaches a noticeable peak at 88%. This rise marks a continuation of a trend observed through the summer months, where humidity levels hovered consistently around 86% from July through August. In contrast to the drier spring months, where humidity dipped to as low as 82% in May, the onset of autumn signals a gradual climb, ultimately leading into even more humid autumnal months. By October, humidity further escalates to 89%, setting the stage for the wetter conditions typical of Belfast during the fall. Overall, September serves as a bridge between the lingering warmth of summer and the cooler, damper conditions of autumn, underscored by its notable humidity levels.

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, allowing you to see how September's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec87%86%86%85%82%84%86%86%88%89%90%87%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Belfast

As September rolls into Belfast, the UV Index settles at 5, marking a return to the moderate exposure category that echoes the conditions of early spring. Following the high levels experienced in summer, with UV values peaking at 8 in both July and June, this month offers a slight reprieve. The necessary burn time returns to a more manageable 30 minutes, encouraging outdoor activities without the intense summer sun to contend with. As the year progresses toward autumn, sun safety remains essential, albeit with a lower risk than in the height of summer. For those planning to enjoy the beautiful surroundings, keeping an eye on the UV Index can make all the difference. For more detailed insights, visit the Belfast UV Index.

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.
JanFebMarAprMayJunJulAugSepOctNovDec124578865321
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.

September Sunshine in Belfast

September in Belfast brings a delightful transition as summer begins to wane, offering 295 hours of sunshine. This marks a notable decrease from the sun-drenched days of May and June, which basked in 403 and 394 hours, respectively. As the vibrant hues of autumn start to paint the landscape, the month still holds its charm with significantly more sunlight than the drearier months that follow. With October dropping to 232 hours and November plunging to just 115 hours, September serves as a bridge between the lingering warmth of summer and the cooler, darker days ahead, making it a precious time for outdoor strolls and enjoying the fading light.

Monthly Sunshine Duration in Belfast: September Highlighted

The September sunshine duration represents the total number of hours Belfast experiences direct sunlight during the month of September, excluding cloudy or obstructed periods. This chart compares the sunshine duration of September with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec81h150h209h322h403h394h399h349h295h232h115h87h
Data source: Belfast September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Belfast During September

In Belfast, September welcomes the gradual shift towards autumn, and with it, the likelihood of sunny weather dips to 20%. This percentage aligns closely with the summer months, such as August and July, where sunny days also appear less frequently. Interestingly, while spring months like April show much higher chances at 42%, the transition into fall sees a decrease in sun exposure. Overall, September captures the essence of the changing seasons, offering a blend of crisp air and occasional sunshine, making it a charming time despite its relatively low chance of clear skies.

Percentage of Sunny Days in September in Belfast

The chart illustrates the percentage of sunny days in Belfast throughout the year, with September highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often Belfast experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec27%23%20%42%33%23%30%21%20%18%20%14%
Data source: Belfast September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Belfast in September

As summer gracefully transitions into autumn, September in Belfast sees a notable shift in daylight duration, tapering down to 12 hours. This marks a decline from the long, sunlit days of June and July, where residents enjoyed up to 17 hours of daylight. While September still offers ample sunlight, it foreshadows the impending shorter days of October, which will see daylight decrease to 10 hours. The gradual shift highlights the rhythm of seasons in Belfast, where vibrant autumn colors soon replace the lush greens of summer, setting the stage for cozy evenings ahead.

Average Daylight Hours in Belfast for September

The chart illustrates the variation in daylight duration in Belfast throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec7h 56m9h 44m11h 54m14h 7m16h 5m17h 7m16h 34m14h 47m12h 38m10h 26m8h 27m7h 21m
Data source: Belfast daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in Belfast

As summer fades and autumn whispers in, September in Belfast greets us with a gentle breeze, averaging 3.4 m/s (8 mph). This slightly cooler wind speed reflects a gradual shift from the warmer months, where July saw the calmest air at just 2.6 m/s (6 mph). While still moderate, September's winds carry a hint of crispness that foreshadows the seasonal changes ahead. Interestingly, as we look toward October, the winds pick up again, likely invigorated by the impending arrival of autumn’s characteristic gales. Overall, September serves as a delightful transition, bridging the warmth of summer with the refreshing chill of fall.

Average September Wind Speed in Belfast

The chart displays monthly wind speed patterns in Belfast, with values for each month shown alongside September's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how September's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec4.36.24.83.53.93.82.63.23.4 m/s4.75.04.9
Data source: Belfast September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in Belfast Compares to Other Months

The weather in Belfast changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of September's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in Belfast and find detailed weather information for every month.

September and January present stark contrasts in weather. In September, temperatures range from a mild 4°C (39°F) at night to a comfortable 21°C (71°F) during the day, with an average temperature of 13°C (56°F). The month experiences significant rainfall, accumulating to 75 mm (3.0 in) over approximately 15 days, accompanied by high humidity at 88%. In comparison, January brings colder conditions, with temperatures dipping as low as -4°C (26°F) at night and reaching a maximum of 14°C (57°F), averaging around 6°C (43°F). Precipitation is somewhat less in January, totaling 60 mm (2.3 in) over about 10 days, while humidity remains relatively high at 87%. For more details on January's weather, visit Belfast weather in January.

In September, the weather tends to be milder compared to February, with temperatures ranging from a minimum of 4°C (39°F) to a maximum of 21°C (71°F) and an average of 13°C (56°F). The month experiences approximately 75 mm (3.0 in) of precipitation over 15 days, accompanied by a higher humidity level of 88%. In contrast, February is significantly cooler, with temperatures ranging from a minimum of -2°C (28°F) to a maximum of 13°C (56°F), and an average temperature of 6°C (43°F). It also sees slightly more precipitation at 89 mm (3.5 in) over 14 days, with humidity remaining relatively high at 86%. For more detailed information, visit Belfast weather in February.

In comparing the weather of September and March, September features milder temperatures, with a minimum of 4°C (39°F) and an average of 13°C (56°F), peaking at a comfortable 21°C (71°F). Contrastingly, March presents cooler conditions, starting with a minimum of -3°C (27°F) and averaging 7°C (44°F), while the maximum reaches only 16°C (60°F). Both months experience significant precipitation, with September totaling 75 mm (3.0 in) over approximately 15 days, and March slightly higher with 80 mm (3.2 in) across 16 days. Humidity levels are comparable, at 88% in September and 86% in March. For a more detailed look at March weather specifics, you can explore Belfast weather in March.

In comparing the weather between September and April, September tends to be milder, with average temperatures ranging from a minimum of 4°C (39°F) to a maximum of 21°C (71°F). The month experiences more precipitation, averaging 75 mm (3.0 in) over 15 days, and a higher humidity level of 88%. In contrast, April is cooler, with temperatures ranging from a minimum of -1°C (31°F) to a maximum of 18°C (65°F). Although it has less rainfall at 45 mm (1.8 in) over 10 days and slightly lower humidity at 85%, the chill of early spring is still evident. For more details on weather specifics, you can refer to Belfast weather in April.

In comparing the weather of September and May, September tends to be slightly warmer with average temperatures around 13°C (56°F), peaking at 21°C (71°F), while May features a lower average of 11°C (52°F) and a maximum temperature equal to September's at 22°C (71°F). Both months experience a fair amount of precipitation, with September receiving 75 mm (3.0 in) over 15 days, slightly more than May's 66 mm (2.6 in) over 13 days. Additionally, humidity levels are higher in September at 88%, compared to May's 82%, contributing to a damp and cooler feel as summer transitions to autumn. For more detailed information about the weather in May, check out Belfast weather in May.

When comparing the weather in September and June, we can see notable differences in temperature and overall conditions. September experiences a milder temperature range, with a minimum of 4°C (39°F) and a maximum of 21°C (71°F), resulting in an average of 13°C (56°F). In contrast, June offers warmer temperatures, with a minimum of 6°C (43°F) and a maximum of 26°C (79°F), averaging 14°C (57°F). Both months have similar precipitation levels; September sees about 75 mm (3.0 in) over 15 days, while June has just slightly more at 78 mm (3.1 in) across 14 days. Humidity levels are also comparable, with September at 88% and June slightly lower at 84%. For more details, check out Belfast weather in June.

In comparing the weather patterns of September and July, September tends to be cooler with minimum temperatures dropping to 4°C (39°F) and average highs reaching 21°C (71°F). In contrast, July experiences warmer conditions, with temperatures ranging from a minimum of 8°C (47°F) to a maximum of 26°C (78°F). Additionally, while September has slightly less precipitation at 75 mm (3.0 in) over 15 days, July sees a bit more rain at 84 mm (3.3 in) over just one less day. Humidity levels are also comparable, with September at 88% and July slightly lower at 86%. For more details about July weather in Belfast, you can check Belfast weather in July.

In comparing the weather between September and August, we see a notable shift. September features cooler temperatures, with a minimum of 4°C (39°F) and an average of 13°C (56°F), compared to August's milder minimum of 8°C (46°F) and an average of 15°C (59°F). While both months experience similar maximum temperatures of 21°C (71°F), September tends to be wetter, receiving 75 mm (3.0 in) of precipitation over 15 days, whereas August has a higher total of 115 mm (4.5 in) over 19 days. Humidity levels remain relatively high in both months, at 88% in September and 86% in August. For a more detailed look at conditions during this time, check out Belfast weather in August.

September and October weather patterns show a noticeable transition as autumn deepens. In September, temperatures range from a cool 4°C (39°F) at night to a pleasant 21°C (71°F) during the day, averaging 13°C (56°F). Precipitation for the month totals 75 mm (3.0 in) and occurs over 15 days, with humidity levels at 88%. In contrast, October brings colder temperatures, with a minimum of 1°C (35°F), an average of 11°C (52°F), and a maximum of 18°C (65°F). The precipitation increases slightly to 92 mm (3.6 in), while maintaining the same number of wet days. Humidity also remains high at 89%. For a more detailed look at the weather trends, check out Belfast weather in October.

When comparing the weather in September and November, September typically enjoys milder temperatures, with an average high of 21°C (71°F) compared to November's peak of 15°C (59°F). While both months experience significant rainfall, November sees slightly higher precipitation levels at 94 mm (3.7 in), while September averages 75 mm (3.0 in). Additionally, humidity levels are relatively high in both months, with September at 88% and November reaching 90%. This gradual transition from warmer to cooler temperatures highlights the shift from early autumn to late fall. For a more detailed look at November weather specifically, you can check Belfast weather in November.

In September, the weather is notably milder, with average temperatures ranging from a minimum of 4°C (39°F) to a maximum of 21°C (71°F). This month experiences an average of 75 mm (3.0 in) of precipitation over 15 days, alongside a high humidity level of 88%. In contrast, December brings a chillier climate, with average temperatures between -1°C (30°F) and 13°C (56°F). Precipitation increases to 91 mm (3.6 in), also spread over 15 days, but humidity slightly decreases to 86%. For more detailed information, you can check Belfast weather in December.

Compare Belfast's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in Belfast

As September rolls in, Belfast experiences a noticeable shift in weather, characterized by a blend of mild temperatures and heightened humidity that sets it apart from the summer months. With daytime highs around 21°C (71°F) and a cooler average of 13°C (56°F) at night, the transition to autumn becomes evident. Rainfall is frequent, with many days seeing precipitation, contributing to an overall damp atmosphere. While the warmth of summer lingers, September's increased cloud cover and rainy spells hint at the colder months to come. For those looking to understand the broader climate patterns, details can be found at Belfast Climate.