Weather in Cornwall for September 2025
Until now, September 2025 in Cornwall is slightly cooler than the historical average by -0.9 °C.
Expect cooler weather in the next days in Cornwall with the forecast suggesting a temperature of 15.1 °C, lower than the historical average.
In general, the average temperature in Cornwall at the beginning of September is 18.4 °C. As the month progressed, temperatures tended to significantly cool down, reaching an average of 14.3 °C by the end of September.
Cornwall in September brings notable rainfall, with an average of 19 rainy days and a total precipitation of 89.6 mm.
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Cornwall Weather September
Temperatures trend during September in Cornwall
September weather in Cornwall day by day
| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| 1 Sept. |  Patchy rain possible | 18° /14° | 3.3 mm | 4 | |
| 2 Sept. |  Light drizzle | 18° /13° | 3.7 mm | 4 | |
| 3 Sept. |  Sunny | 18° /14° | 3.5 mm | 5 | |
| 4 Sept. | Sunny | 19° /14° | 4.6 mm | 5 | |
| 5 Sept. |  Partly cloudy | 18° /14° | 5.2 mm | 5 | |
| 6 Sept. | Patchy rain possible | 19° /15° | 10.2 mm | 5 | |
| 7 Sept. |  Patchy light rain with thunder | 19° /14° | 5.2 mm | 4 | |
| 8 Sept. | Partly cloudy | 18° /15° | 1 mm | 5 | |
| 9 Sept. | Partly cloudy | 18° /14° | 6.4 mm | 4 | |
| 10 Sept. | Light rain shower | 18° /14° | 3.7 mm | 4 | |
| 11 Sept. | Patchy rain possible | 16° /13° | 2.9 mm | 4 | |
| 12 Sept. |  Overcast | 15° /12° | 3.7 mm | 4 | |
| 13 Sept. |  Cloudy | 15° /11° | 2.1 mm | 4 | |
| 14 Sept. | Overcast | 17° /11° | 1.9 mm | 4 | |
| 15 Sept. | Overcast | 18° /12° | 0 mm | 4 | |
| 16 Sept. | Patchy rain possible | 16° /14° | 2.1 mm | 0.8 | |
| 17 Sept. |  Moderate rain | 17° /14° | 5.2 mm | 0.3 | |
| 18 Sept. | Partly cloudy | 19° /15° | 0 mm | 1 | |
| 19 Sept. | Patchy rain possible | 20° /15° | 0.3 mm | 0.9 | |
| 20 Sept. | Patchy rain possible | 15° /13° | 1.1 mm | 0.6 | |
| 21 Sept. | Patchy rain possible | 13° /11° | 3.2 mm | 3 | |
| 22 Sept. | Patchy rain possible | 13° /11° | 0.3 mm | 3 | |
| 23 Sept. | Patchy rain possible | 14° /11° | 0.3 mm | 3 | |
| 24 Sept. | Partly cloudy | 14° /11° | 0.1 mm | 4 | |
| 25 Sept. | Sunny | 14° /9° | 0 mm | 4 | |
| 26 Sept. | Sunny | 14° /11° | 0 mm | 4 | |
| 27 Sept. | Overcast | 14° /11° | 0 mm | 3 | |
| 28 Sept. | Moderate rain | 13° /11° | 5.1 mm | 3 | |
| 29 Sept. | Patchy rain possible | 15° /12° | 0.7 mm | 3 | |
| 30 Sept. | Overcast | 16° /12° | 1 mm | 4 | |
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Cornwall in September - FAQ
Cornwall water temperatures in September
The average water temperature of the Atlantic Ocean near Cornwall in September is 15.7 °C. Temperatures remain fairly consistent throughout the month.
- What is the water temperature in Cornwall in September?
- The average water temperature in Cornwall in September is 15.7 °C.
- Can you swim in Cornwall in September?
- Brisk: quick dips and active swimming are fine, but pack a 2–3 mm spring suit if you plan longer sessions or early-morning outings.
September rainfall patterns in Cornwall
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Where is Cornwall?Get accurate weather forecasts for Cornwall, located at latitude 50.416 and longitude -5.073. Stay updated with localized weather information tailored for Cornwall.