Letterkenny Weather in September
During September, Letterkenny experiences moderate daytime temperatures of 17°C (63°F) and cooler nights around 10°C (50°F). Expect quite a bit of rainfall. Around 99 mm (3.9 in) is typical.
Rainfall in Letterkenny in September
On average, there are about 22 days with rain during this month, averaging 99 mm (3.9 in). Expect plenty of grey, overcast days rather than intense storms. The rain rarely amounts to much on any given day.
Temperature in Letterkenny in September
September in Letterkenny brings moderate temperatures, with highs of 17°C (63°F) and nights around 10°C (50°F). This creates a mild day-to-night pattern that is generally easy to manage with the right clothing. Nights cool down to 10°C (50°F), so a light jacket or extra layer is useful once the sun goes down. On the plus side, the cooler nights make for comfortable sleeping conditions.
Sunshine in Letterkenny in September
The area enjoys a balanced 118 hours of sunlight, ensuring it's neither too overcast nor too sunny.Our weather planner can help you find worldwide destinations with pleasant weather during this period. May, July, August and September typically offer the best weather for Letterkenny.
Letterkenny Temperature in September
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Letterkenny Weather by Month
Pick a month to see the average temperature, rainfall and sunshine in Letterkenny - and find the best time to visit.
Daily Historical Temperatures
50-year average (1976-2025)
Based on our historical records, temperatures in Letterkenny typically stay consistent throughout September, with daily highs averaging around 17°C (63°F). Nights are cool, with lows typically ranging from 9°C (48°F) to 11°C (52°F).
Average temperatures in September
Daily Historical Precipitation
50-year average (1976-2025)
Average daily rainfall for each day of the month based on long-term records.
Average precipitation in September
Historical weather records for Letterkenny in September
Browse day-by-day weather records for Letterkenny spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.
Letterkenny historical weather extremes in September
The extremes listed below come from historical weather data collected in Letterkenny from 1976 through 2025.
- Letterkenny recorded its highest September temperature of 27°C (81°F) on September 7, 2023.
- The lowest daytime temperature in September was 10°C (50°F), recorded on September 26, 2024.
- The coldest night in September in Letterkenny was on September 27, 2020, with a minimum of 1°C (34°F).
- The wettest September day on record brought 41 mm (1.6 in) of precipitation to Letterkenny (September 6, 2010).
Best Places in Ireland in September
Find out more about the weather in Ireland and which places have the best travel conditions in this month. See all of Ireland in September →
Perfect weather is subjective. On this map perfect weather has been defined with temperatures between 20°C (68°F) and 29°C (84°F) and not too much precipitation (less than 90 mm (3.5 in) a month).
What to Wear in Letterkenny in September
Pleasant temperatures in September mean you can pack light but flexibel pieces. Think cotton t-shirts, comfortable walking shorts, and one warmer layer for evenings. A light sweater or denim jacket works well. Prepare for significant rainfall with proper waterproof clothing and shoes. Sunglasses could come in handy during the sunnier parts of your trip.
What To Do in Letterkenny in September
We rated the following activities from 1 (least suitable) to 10 (best) to do.
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Swimming5/10 -
Cycling6/10 -
Walking6/10 -
Camping8/10 -
Outdoor sports9/10
Letterkenny 3-Day Forecast
See the full Letterkenny climate overview or explore weather in Ireland.
Popular in September
Where to go in September - average daytime high across popular destinations.
Westport
17°C (63°F) Doolin17°C (63°F) Kilkenny
18°C (64°F) Cork18°C (64°F) Kenmare18°C (64°F) Killarney17°C (63°F) Galway18°C (64°F) Dublin18°C (64°F) 
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