Click on a day for an hourly weather forecast
The temperatures in Carmarthen in September are usually low and can range between 11°C and 17°C.
You can expect about 3 to 8 days of rain in Carmarthen during the month of September. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.
Our weather forecast can give you a great sense of what weather to expect in Carmarthen in September 2025.
If you’re planning to visit Carmarthen in the near future, we highly recommend that you review the 14 day weather forecast for Carmarthen before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | 8° / 4° | 11 | 18 | 2 | 136 mm | Awful | Carmarthen in January |
| February | 8° / 4° | 9 | 17 | 2 | 97 mm | Awful | Carmarthen in February |
| March | 10° / 4° | 7 | 24 | 0 | 79 mm | Bad | Carmarthen in March |
| April | 12° / 5° | 6 | 24 | 0 | 63 mm | Ok | Carmarthen in April |
| May | 14° / 8° | 6 | 25 | 0 | 79 mm | Good | Carmarthen in May |
| June | 17° / 10° | 7 | 23 | 0 | 93 mm | Ok | Carmarthen in June |
| July | 18° / 12° | 6 | 25 | 0 | 96 mm | Good | Carmarthen in July |
| August | 18° / 13° | 7 | 24 | 0 | 102 mm | Ok | Carmarthen in August |
| September | 17° / 11° | 6 | 24 | 0 | 98 mm | Good | Carmarthen in September |
| October | 14° / 10° | 8 | 23 | 0 | 124 mm | Ok | Carmarthen in October |
| November | 11° / 7° | 10 | 20 | 0 | 138 mm | Bad | Carmarthen in November |
| December | 9° / 5° | 11 | 19 | 1 | 147 mm | Bad | Carmarthen in December |