September is one of the warmer months of the year in Llanelli, with average highs near 16.8°C and lows around 13.5°C (mean 15.2°C). It is about average for rainfall, averaging 93 mm of rainfall and 84% relative humidity across the period.
September is one of the warmer months of the year in Llanelli. Across 45 years of records, the warmest September in Llanelli was 2023 — when the month averaged 17.4°C — while the coldest was 1986 at 12.9°C. Typical September days reach 16.8°C with nights near 13.5°C. The long-term trend is warming, about 0.3°C per decade.
September is about average for rainfall in Llanelli, averaging 93 mm of rainfall. The wettest September on record was 2019 with 183 mm, while the driest was 1986 at 23 mm.
Relative humidity in Llanelli during September averages 84%. The most humid September was 2006 at 87%, and the least humid was 1990 at 80%.
September receives about 3.3 kWh/m²/day of solar energy in Llanelli. The sunniest September was 2014 at 3.9 kWh/m²/day, and the cloudiest was 2000 at 2.7.
Average wind speed in Llanelli during September is 4.9 m/s. The windiest September was 1983 at 6 m/s, while the calmest was 2014 at 3.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 14.7°C | 14.9°C | 15.4°C | 15.2°C | 15.9°C | +1.2°C |
| Avg High | 16.4°C | 16.6°C | 17.1°C | 16.8°C | 17.6°C | +1.2°C |
| Avg Low | 13.1°C | 13.2°C | 13.7°C | 13.6°C | 14.3°C | +1.2°C |
| Avg Rain | 91 mm | 91 mm | 68 mm | 105 mm | 122 mm | +31 mm |
September temperatures in Llanelli have risen by about 1°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 8.6°C (1986) to a record high of 24°C (2023).
Rainfall in September is about average for rainfall, averaging 93 mm, with a wettest year of 183 mm.
One of the best times to visit Llanelli
September is one of the best times to visit Llanelli. Expect days averaging 16.8°C and nights around 13.5°C (mean 15.2°C) — warmer than Llanelli's yearly average — with higher rainfall (93 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 16.8°C | 15.3°C | 13.8°C | 19.7°C | 10.4°C | 167 mm | 82% | 5.4 m/s | 3.4 |
| 2024 | 16.8°C | 15.1°C | 13.4°C | 20.6°C | 10.7°C | 147 mm | 85% | 4.7 m/s | 2.8 |
| 2023 🔥 | 19.1°C | 17.4°C | 15.6°C | 24.0°C | 12.0°C | 112 mm | 86% | 4.6 m/s | 3.2 |
| 2022 | 17.5°C | 15.9°C | 14.4°C | 20.8°C | 11.6°C | 115 mm | 83% | 4.8 m/s | 3.1 |
| 2021 | 18.2°C | 16.5°C | 14.8°C | 22.6°C | 11.7°C | 105 mm | 86% | 3.8 m/s | 3.1 |
| 2020 | 17.0°C | 15.3°C | 13.6°C | 20.6°C | 10.4°C | 89 mm | 84% | 4.8 m/s | 3.4 |
| 2019 🌧️ | 17.3°C | 15.7°C | 14.1°C | 20.2°C | 11.8°C | 183 mm | 85% | 5.5 m/s | 3.4 |
| 2018 | 16.6°C | 14.9°C | 13.3°C | 19.8°C | 10.7°C | 115 mm | 82% | 5.1 m/s | 3.3 |
| 2017 | 16.3°C | 14.9°C | 13.5°C | 18.2°C | 11.6°C | 160 mm | 85% | 5.6 m/s | 3.2 |
| 2016 | 17.5°C | 16.1°C | 14.7°C | 20.9°C | 12.8°C | 122 mm | 86% | 5.1 m/s | 3.1 |
| 2015 | 15.9°C | 14.2°C | 12.4°C | 18.7°C | 10.9°C | 88 mm | 83% | 4.7 m/s | 3.7 |
| 2014 | 18.1°C | 16.2°C | 14.2°C | 20.2°C | 12.1°C | 25 mm | 84% | 3.4 m/s | 3.9 |
| 2013 | 16.8°C | 15.1°C | 13.3°C | 19.6°C | 11.3°C | 68 mm | 85% | 4.6 m/s | 3 |
| 2012 | 15.6°C | 14.1°C | 12.6°C | 18.6°C | 9.7°C | 86 mm | 84% | 5.3 m/s | 3.3 |
| 2011 | 16.8°C | 15.4°C | 14.0°C | 20.2°C | 12.2°C | 89 mm | 86% | 5.9 m/s | 3.1 |
| 2010 | 16.6°C | 15.0°C | 13.4°C | 19.1°C | 9.3°C | 111 mm | 85% | 5 m/s | 3.2 |
| 2009 | 16.8°C | 14.9°C | 13.0°C | 18.7°C | 11.0°C | 38 mm | 84% | 4.6 m/s | 3.4 |
| 2008 | 16.3°C | 14.8°C | 13.2°C | 17.7°C | 11.3°C | 99 mm | 84% | 4.6 m/s | 3.3 |
| 2007 | 16.8°C | 15.1°C | 13.5°C | 20.1°C | 8.7°C | 52 mm | 86% | 4.8 m/s | 3.6 |
| 2006 | 18.4°C | 16.7°C | 15.0°C | 20.5°C | 13.2°C | 57 mm | 87% | 5.1 m/s | 3.4 |
| 2005 | 17.6°C | 15.8°C | 13.9°C | 21.1°C | 11.1°C | 78 mm | 85% | 4.6 m/s | 3.4 |
| 2004 | 17.2°C | 15.7°C | 14.2°C | 21.9°C | 12.1°C | 74 mm | 85% | 5.9 m/s | 3.3 |
| 2003 | 17.3°C | 15.5°C | 13.7°C | 20.1°C | 10.5°C | 47 mm | 82% | 3.9 m/s | 3.5 |
| 2002 | 17.3°C | 15.3°C | 13.3°C | 20.0°C | 11.2°C | 33 mm | 83% | 3.9 m/s | 3.6 |
| 2001 | 16.2°C | 14.7°C | 13.2°C | 18.6°C | 11.0°C | 62 mm | 85% | 5.2 m/s | 3.3 |
| 2000 | 17.2°C | 15.8°C | 14.3°C | 20.9°C | 10.2°C | 144 mm | 86% | 4.8 m/s | 2.7 |
| 1999 | 17.6°C | 16.0°C | 14.3°C | 22.0°C | 12.6°C | 137 mm | 85% | 4.7 m/s | 3.3 |
| 1998 | 17.1°C | 15.6°C | 14.1°C | 19.9°C | 11.4°C | 107 mm | 87% | 5.3 m/s | 3.2 |
| 1997 | 17.2°C | 15.4°C | 13.6°C | 19.6°C | 11.3°C | 41 mm | 86% | 4.7 m/s | 3.2 |
| 1996 | 16.8°C | 14.8°C | 12.9°C | 19.4°C | 10.5°C | 45 mm | 82% | 4.8 m/s | 3.7 |
| 1995 | 16.5°C | 14.9°C | 13.3°C | 19.3°C | 10.9°C | 83 mm | 82% | 4.9 m/s | 3.5 |
| 1994 | 15.4°C | 13.9°C | 12.4°C | 17.7°C | 10.6°C | 133 mm | 85% | 5.2 m/s | 3 |
| 1993 | 15.5°C | 13.9°C | 12.3°C | 19.6°C | 10.3°C | 109 mm | 83% | 4.7 m/s | 3.3 |
| 1992 | 15.5°C | 14.0°C | 12.5°C | 18.6°C | 10.6°C | 105 mm | 85% | 5.3 m/s | 3.1 |
| 1991 | 17.9°C | 15.9°C | 13.9°C | 21.8°C | 10.6°C | 91 mm | 82% | 4.6 m/s | 3.6 |
| 1990 | 16.6°C | 14.6°C | 12.7°C | 19.6°C | 9.8°C | 60 mm | 80% | 4.7 m/s | 3.5 |
| 1989 | 17.4°C | 15.5°C | 13.7°C | 20.3°C | 11.9°C | 70 mm | 83% | 4.6 m/s | 3 |
| 1988 | 15.6°C | 14.0°C | 12.5°C | 20.6°C | 9.3°C | 84 mm | 85% | 5.4 m/s | 3.2 |
| 1987 | 16.4°C | 14.8°C | 13.3°C | 18.5°C | 9.8°C | 85 mm | 84% | 4.7 m/s | 3.4 |
| 1986 ❄️ | 14.7°C | 12.9°C | 11.1°C | 16.2°C | 8.6°C | 23 mm | 81% | 3.9 m/s | 3.4 |
| 1985 | 16.7°C | 15.1°C | 13.4°C | 19.4°C | 11.0°C | 64 mm | 87% | 4.6 m/s | 3.2 |
| 1984 | 16.2°C | 14.6°C | 13.1°C | 20.2°C | 10.4°C | 128 mm | 81% | 5.5 m/s | 3.3 |
| 1983 | 16.2°C | 14.7°C | 13.2°C | 18.9°C | 10.7°C | 114 mm | 85% | 6 m/s | — |
| 1982 | 17.0°C | 15.2°C | 13.5°C | 21.7°C | 11.3°C | 103 mm | 86% | 4.4 m/s | — |
| 1981 | 17.2°C | 15.6°C | 14.0°C | 19.9°C | 11.6°C | 153 mm | 83% | 5 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 16.8°C with lows near 13.5°C (mean 15.2°C), based on 45 years of NASA POWER data.
September averages 93 mm of rainfall in Llanelli, about average for rainfall. The wettest on record was 183 mm in 2019.
The hottest September reached 24°C in 2023. The coldest dipped to 8.6°C in 1986.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1°C. Daytime highs moved from 16.7°C to 17.7°C and overnight lows from 13.4°C to 14.4°C over the same span.
September is one of the warmer months of the year in Llanelli and about average for rainfall, so plan for around 16.8°C daytime highs and 13.5°C at night.
Not quite — September is the 10th coolest month in Llanelli, averaging 15.2°C.
For September in Llanelli, pack light layers you can adjust through the day, with typical highs of 16.8°C and lows of 13.5°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 84% — quite humid.
Average wind speed in September is 4.9 m/s. The windiest September on record averaged 6 m/s (1983).
The wettest September on record was 2019 with 183 mm. On average, September sees 93 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Llanelli behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
