Click on a day for an hourly weather forecast
The temperatures in Letterkenny in September are quite cold with temperatures between 8°C and 16°C, warm clothes are a must.
You can expect about 3 to 8 days of rain in Letterkenny 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 Letterkenny in September 2025.
If you’re planning to visit Letterkenny in the near future, we highly recommend that you review the 14 day weather forecast for Letterkenny before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | 6° / 1° | 9 | 18 | 4 | 78 mm | Awful | Letterkenny in January |
| February | 7° / 1° | 9 | 15 | 4 | 77 mm | Awful | Letterkenny in February |
| March | 9° / 2° | 8 | 21 | 3 | 66 mm | Awful | Letterkenny in March |
| April | 12° / 3° | 5 | 24 | 1 | 48 mm | Ok | Letterkenny in April |
| May | 14° / 5° | 6 | 25 | 0 | 69 mm | Good | Letterkenny in May |
| June | 17° / 8° | 6 | 24 | 0 | 78 mm | Good | Letterkenny in June |
| July | 18° / 10° | 7 | 24 | 0 | 90 mm | Ok | Letterkenny in July |
| August | 17° / 10° | 6 | 25 | 0 | 76 mm | Good | Letterkenny in August |
| September | 16° / 8° | 6 | 24 | 0 | 59 mm | Good | Letterkenny in September |
| October | 13° / 6° | 8 | 23 | 0 | 79 mm | Bad | Letterkenny in October |
| November | 9° / 4° | 8 | 21 | 0 | 80 mm | Bad | Letterkenny in November |
| December | 7° / 2° | 8 | 21 | 2 | 76 mm | Awful | Letterkenny in December |