Last updated: August 23, 2025
In Letterkenny, Ireland, the average temperature in September hovers around 13°C (55°F), with daily variations ranging from a cool 3°C (37°F) to a pleasant 24°C (76°F). This month experiences significant precipitation, totaling 104 mm (4.1 in) across 19 days of rain. Expect high humidity levels at 87%, which can make the atmosphere feel quite damp and refreshing!
In September in Letterkenny, the average temperature is 13°C (55°F). Maximums can reach 24°C (76°F) and minimums can be as low as 3°C (37°F). This range makes it a great time for travelers to enjoy a mix of mild weather and comfortable conditions while exploring the area.
In Letterkenny in September, the precipitation amount is 104 mm (4.1 in) over the course of 19 days.
In Letterkenny in September, humidity is 87%. With an average temperature of 13°C (55°F), this humidity feels like a heavy blanket wrapping around you, making travel sluggish and slightly uncomfortable, as each step seems to cling to the damp air.
In Letterkenny in September, the maximum UV index reaches 5, which corresponds to a moderate Exposure Category. Under these conditions, the estimated time to burn is approximately 30 minutes. For more details, you can check the Hourly UV Index in Letterkenny.
UV Risk Categories
Weather in Letterkenny varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Letterkenny, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | 6°C (43°F) | 85 mm (3.3 inches) | 84% | low |
| February Weather | 6°C (42°F) | 123 mm (4.8 inches) | 84% | low |
| March Weather | 6°C (44°F) | 111 mm (4.4 inches) | 83% | moderate |
| April Weather | 8°C (47°F) | 59 mm (2.3 inches) | 84% | moderate |
| May Weather | 11°C (52°F) | 81 mm (3.2 inches) | 83% | high |
| June Weather | 13°C (56°F) | 102 mm (4.0 inches) | 83% | very high |
| July Weather | 15°C (59°F) | 98 mm (3.9 inches) | 86% | very high |
| August Weather | 14°C (58°F) | 146 mm (5.8 inches) | 86% | high |
| September Weather | 13°C (55°F) | 104 mm (4.1 inches) | 87% | moderate |
| October Weather | 10°C (51°F) | 124 mm (4.9 inches) | 87% | moderate |
| November Weather | 8°C (46°F) | 108 mm (4.2 inches) | 88% | low |
| December Weather | 6°C (44°F) | 124 mm (4.9 inches) | 84% | low |