September Weather in Caernarfon, United Kingdom

Last updated: March 17, 2025

September in Caernarfon, United Kingdom, presents a whimsical mix of weather, characterized by a maximum temperature reaching a warm 27°C (81°F), offering a brief taste of summer's end. The average temperature settles at a comfortable 14°C (57°F), while cooler days can dip to a minimum of 3°C (38°F). With 98 mm (3.9 in) of rain falling across 15 days, this month witnesses a significant amount of precipitation, contributing to the region's lush landscape. The high humidity level of 85% adds to the overall feeling of a rich, vibrant atmosphere, making September a diverse and interesting time to experience Caernarfon’s unique charm.

September Temperature in Caernarfon

In September, Caernarfon experiences a delightful transition as summer fades into autumn. With minimum temperatures averaging a mild 3°C (38°F), the days remain pleasantly warm, boasting an average of 14°C (57°F) and reaching peaks around 27°C (81°F). This marks a gradual cooling trend from the warmer summer months, yet it retains a comfortable feel, allowing for enjoyable outdoor activities. As the warmth begins to wane, the crispness in the air hints at the approaching fall, making September a beautiful time to explore the scenic landscapes of this historic town.

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

The chart illustrates September temperature patterns in Caernarfon, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends.
JanFebMarAprMayJunJulAugSepOctNovDec434445485358616057524745
Data source: Temperature data for Caernarfon 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 Caernarfon

September in Caernarfon, United Kingdom, experiences a significant amount of rainfall, with 98 mm (3.9 in) recorded over 15 days. This marks a slight decrease compared to August's 105 mm (4.1 in), yet remains relatively high within the annual precipitation trends. As the summer season transitions to autumn, September's rainfall serves as a precursor to the wetter months ahead, notably October, which sees an uptick to 128 mm (5.1 in). The consistency in rainy days throughout September reflects the lingering dampness from late summer, setting a tone for the coming months when precipitation peaks, often reaching over 120 mm in each of the final three months of the year. This trend emphasizes the region's characteristic maritime climate, where rain is a frequent companion, especially as temperatures cool.

September Precipitation Trends in Caernarfon

The chart displays monthly precipitation patterns in Caernarfon, 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.
JanFebMarAprMayJunJulAugSepOctNovDec771031045571918210598128111129
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Caernarfon

In September, Caernarfon experiences a notable rise in humidity, reaching 85%, a slight increase compared to the preceding summer months. This uplift marks a transition towards the wetter autumn season, as humidity levels have generally decreased from the high of 89% in January to a summertime low of 78% in July. The overall trend illustrates a gradual return to the higher humidity typical of the fall and winter months, with October expected to bring even more moisture at 90%. As the year progresses, Caernarfon’s humidity pattern reflects the area's maritime climate, characterized by significant fluctuations that contribute to its lush landscapes.

September Average Humidity in Caernarfon

This chart illustrates the average monthly humidity levels in Caernarfon, 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.
JanFebMarAprMayJunJulAugSepOctNovDec89%88%86%85%79%81%78%79%85%90%91%89%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Caernarfon

As September rolls into Caernarfon, the UV Index reflects a noticeable shift from the summer months. With a moderate UV Index of 5, outdoor enthusiasts should be mindful of sun exposure, as the burn time is approximately 30 minutes. This is a drop from the peak summer values, where UV readings soared to 8 in June and July, indicating very high exposure risk. As daylight begins to wane and autumn approaches, it's essential to maintain awareness of changing UV levels, even when temperatures are cooling. For more detailed insights and trends on UV levels throughout the year, visit Caernarfon UV Index.

Maximum UV Index Levels in Caernarfon for September

The chart shows the monthly maximum UV Index (UVI) for Caernarfon 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.
JanFebMarAprMayJunJulAugSepOctNovDec124578875421
Data source: Caernarfon 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 Caernarfon

September in Caernarfon, United Kingdom, brings a delightful respite as the summer sun lingers just a bit longer, boasting 315 hours of sunshine—a significant drop from the sun-soaked August but still comfortably above the winter months. This month marks a transition from the peak of July's impressive 421 hours, showcasing a typical pattern where daylight gradually wanes as autumn approaches. However, September's sunshine continues to outshine both October and the winter months, suggesting a gentle farewell to summer that invites locals and visitors alike to enjoy the crisp air and lingering warmth during early autumn strolls by the harbor. With a steady decline in daylight heading into the colder months, now is the perfect time to soak up every golden hour in this charming coastal town.

Monthly Sunshine Duration in Caernarfon: September Highlighted

The September sunshine duration represents the total number of hours Caernarfon 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.
JanFebMarAprMayJunJulAugSepOctNovDec93h162h228h335h415h404h421h383h315h238h126h109h
Data source: Caernarfon September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Caernarfon During September

In Caernarfon, United Kingdom, the likelihood of experiencing sunny weather dips notably in September, with only a 20% chance of sunshine, making it one of the cloudier months of the year. This marks a decline from the 46% chance seen in April, the peak of spring. Following the summer, where July offers a comparatively higher 35% chance, September's reduced sun exposure signals the shift toward autumn, as the already variable weather patterns become increasingly unpredictable. As the days grow shorter and temperatures begin to cool, residents and visitors alike should prepare for a fall season where sunbeams become more fleeting.

Percentage of Sunny Days in September in Caernarfon

The chart illustrates the percentage of sunny days in Caernarfon 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 Caernarfon experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec22%25%25%46%30%25%35%24%20%17%19%23%
Data source: Caernarfon September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Caernarfon in September

As the vibrant summer days gradually fade, September in Caernarfon showcases a delightful blend of lingering light and the onset of autumn. With 12 hours of daylight, this month marks a natural transition from the peak brightness of June and July, which basked in 16 hours of sunshine. Though daylight begins to wane, the welcoming 12 hours still provide ample opportunity for outdoor activities and enjoying the stunning landscapes. As we move further into the year, the days will continue to shorten, but September’s light remains a cherished feature before the crisp shadows of autumn fully take hold.

Average Daylight Hours in Caernarfon for September

The chart illustrates the variation in daylight duration in Caernarfon throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec8h 8m9h 50m11h 54m14h 1m15h 53m16h 52m16h 20m14h 39m12h 37m10h 31m8h 37m7h 36m
Data source: Caernarfon daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in Caernarfon

As summer gives way to autumn, September in Caernarfon experiences a gentle shift in wind patterns. With an average wind speed of 3.3 m/s (7 mph), September marks a decrease compared to the more blustery summer months, reflecting a seasonal transition. This softer breeze, akin to a whisper of change, paves the way for the brisk October winds that follow, which pick up to 5.5 m/s (12 mph). The month serves as a bridge, blending the lingering warmth of late summer with the refreshing chill of approaching fall, creating an inviting atmosphere for those who enjoy the outdoors. While the winds may ease in September, the anticipation of the more dynamic autumn gales is already palpable.

Average September Wind Speed in Caernarfon

The chart displays monthly wind speed patterns in Caernarfon, 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.
JanFebMarAprMayJunJulAugSepOctNovDec4.65.85.23.34.03.82.73.83.3 m/s5.54.85.0
Data source: Caernarfon September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in Caernarfon Compares to Other Months

The weather in Caernarfon 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 Caernarfon and find detailed weather information for every month.

In comparing the weather of September and January, September presents a much warmer climate, with temperatures ranging from a chilly 3°C (38°F) to a comfortable high of 27°C (81°F), and an average of 14°C (57°F). The month has a significant amount of precipitation as well, totaling 98 mm (3.9 in) over approximately 15 days, resulting in a humidity level of 85%. In contrast, January brings much colder conditions, with temperatures dipping as low as -3°C (27°F) and averaging around 6°C (43°F). While it experiences slightly less precipitation at 77 mm (3.0 in) over 13 days, the humidity is relatively high at 89%. For a detailed look at January's weather, you can visit Caernarfon weather in January.

When comparing the weather in September and February, there are some notable differences. September typically offers milder temperatures, with averages around 14°C (57°F) and maximums reaching up to 27°C (81°F), making it generally more pleasant. In contrast, February sees colder conditions, with an average temperature of 6°C (44°F) and minimums dropping to -4°C (26°F). Both months experience relatively high levels of rainfall, with September having 98 mm (3.9 in) over 15 days and February slightly wetter at 103 mm (4.1 in) over 16 days. Humidity levels are also quite similar, with September at 85% and February at 88%. For more detailed weather information, you can check out Caernarfon weather in February.

When comparing the weather in September and March, we see notable differences in temperature and precipitation. September typically enjoys milder temperatures, with a minimum of 3°C (38°F) and an average of 14°C (57°F), reaching a maximum of 27°C (81°F). In contrast, March experiences colder conditions, starting with a minimum of -5°C (23°F) and averaging 7°C (45°F), while peaking at 18°C (65°F).

Both months see significant precipitation, with September averaging 98 mm (3.9 in) over 15 days and March slightly higher at 104 mm (4.1 in) over 18 days. Humidity remains similar, with September at 85% and March at 86%. For more specific details about March weather conditions, you can check Caernarfon weather in March.

September and April present distinct weather patterns, reflecting the transition from summer to autumn and the arrival of spring, respectively. In September, temperatures can range from a chilly 3°C (38°F) to a warm 27°C (81°F), with an average of 14°C (57°F) and higher humidity at 85%. The month typically experiences around 98 mm (3.9 in) of precipitation over 15 days. In contrast, April sees cooler temperatures, with a range from -1°C (31°F) to a maximum of 22°C (72°F) and an average of 9°C (48°F). It has less precipitation at 55 mm (2.2 in) over 11 days, while maintaining a similar humidity level at 84%. For more information on April weather, you can visit Caernarfon weather in April.

When comparing the weather in September and May, we observe distinct differences. September typically experiences a wider temperature range, with a minimum of 3°C and maximum of 27°C, resulting in an average of 14°C. In contrast, May has slightly cooler temperatures, with a minimum of 0°C and a maximum of 28°C, averaging 12°C. Additionally, September is marked by higher precipitation at 98 mm over 15 days, while May receives less rainfall, at 71 mm over 12 days. Humidity levels are also higher in September, reaching 85%, compared to 79% in May. For more detailed weather information specific to May, you can visit Caernarfon weather in May.

In comparing the weather between June and September, we see some notable differences. June typically enjoys slightly warmer temperatures, with a minimum of 5°C (41°F) and a maximum of 29°C (84°F), while September has a minimum of 3°C (38°F) and a maximum of 27°C (81°F). Both months experience significant humidity, with September being slightly more humid at 85% compared to June's 81%. When it comes to precipitation, September has a bit more with 98 mm (3.9 in) over 15 days, whereas June sees 91 mm (3.6 in) across 14 days. For more detailed information, you can check out Caernarfon weather in June.

In comparing the weather between September and July, we see notable differences in temperature and precipitation patterns. September experiences a broader temperature range, with a minimum of 3°C (38°F) and a maximum reaching 27°C (81°F), while July maintains milder conditions with temperatures ranging from a minimum of 7°C (45°F) to a maximum of 29°C (85°F). Additionally, September is slightly wetter, accumulating 98 mm (3.9 in) of precipitation over 15 days, compared to July's 82 mm (3.2 in) in the same number of days. Humidity levels are also higher in September at 85%, compared to 78% in July. For more detailed information, check Caernarfon weather in July.

September weather showed a notable shift compared to August, with minimum temperatures dropping significantly from 8°C (46°F) in August to just 3°C (38°F). While the average temperature in September was slightly lower at 14°C (57°F), the maximum temperature increased marginally to 27°C (81°F), just above August's maximum of 26°C (79°F). Rainfall also varied, with September recording 98 mm (3.9 in) of precipitation over 15 days, compared to 105 mm (4.1 in) over 19 days in August. Additionally, September exhibited higher humidity levels at 85%, compared to August’s 79%. For a closer look at the weather specifics in August, visit Caernarfon weather in August.

September and October present a notable shift in weather patterns. In September, temperatures range from a mild 3°C (38°F) at night to a comfortable 27°C (81°F) during the day, with an average of 14°C (57°F). The month sees approximately 98 mm (3.9 in) of precipitation over 15 days, accompanied by a humidity level of 85%. In contrast, October experiences colder temperatures, with nightly lows dropping to -2°C (29°F) and daytime highs peaking at 22°C (71°F), averaging around 11°C (53°F). Additionally, October brings increased rainfall, totaling 128 mm (5.1 in) over 18 days, and slightly higher humidity at 90%. For those interested in more detailed weather information for this month, Caernarfon weather in October offers a comprehensive overview.

September and November weather conditions exhibit notable contrasts. In September, temperatures range from a minimum of 3°C (38°F) to a maximum of 27°C (81°F), with an average of 14°C (57°F). The month sees about 98 mm (3.9 in) of precipitation over 15 days, with humidity levels around 85%. In contrast, November experiences cooler temperatures, with a minimum of -1°C (31°F), an average of 9°C (48°F), and a maximum of 15°C (60°F). Precipitation increases slightly to 111 mm (4.4 in) over 19 days, and humidity rises to 91%. For more detailed insights into November weather, check out Caernarfon weather in November.

September and December exhibit significant differences in weather characteristics. In September, temperatures range from a mild 3°C (38°F) at night to a pleasant high of 27°C (81°F) during the day, with average conditions around 14°C (57°F). This month experiences about 98 mm (3.9 in) of rainfall spread over 15 days and has a humidity level of 85%. In contrast, December welcomes the cold, with nighttime temperatures dipping to -1°C (30°F) and daytime highs averaging around 7°C (45°F), peaking at 13°C (56°F). Precipitation increases to 129 mm (5.1 in) over 20 days, with humidity slightly higher at 89%. For more detailed information, you can check the Caernarfon weather in December.

Compare Caernarfon's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in Caernarfon

In September, Caernarfon experiences a notable transition in weather as summer bids farewell, leading to a mix of warm days and chilly nights. With temperatures ranging from mild highs to cold lows, it marks a departure from the more stable heat of the summer months. The increased rainfall and humidity levels reveal a shift towards the wetter fall season, with significant chances of precipitation on about half the days. As nature begins to prepare for autumn, the landscape transforms, adding a crispness to the air that invigorates visitors. For a deeper understanding of how Caernarfon's climate evolves throughout the year, explore Caernarfon Climate.