Ireland: where to swim in September?
Ireland, in September: the sea is at 15.0 °C on average along the coast, from 14.2 °C to 15.7 °C depending on the spot. Where the water is warmest (15.7 °C), it is cool. Swimming is fine if you like cool water: you get used to it after a few minutes, especially in mild weather.
Sea temperature, month by month
| Month | Average temperature | Depending on the spot | Where it is warmest |
|---|---|---|---|
| January | 9.9 °C | 9.2 °C – 10.4 °C | cold |
| February | 9.4 °C | 8.5 °C – 10.2 °C | cold |
| March | 9.4 °C | 8.5 °C – 10.2 °C | cold |
| April | 10.0 °C | 9.2 °C – 10.6 °C | cold |
| May | 11.5 °C | 10.8 °C – 12.1 °C | cold |
| June | 13.6 °C | 12.9 °C – 14.5 °C | cold |
| July | 15.2 °C | 14.2 °C – 16.4 °C | cool |
| August | 15.8 °C | 14.9 °C – 16.5 °C | cool |
| September | 15.0 °C | 14.2 °C – 15.7 °C | cool |
| October | 13.7 °C | 12.9 °C – 14.3 °C | cold |
| November | 12.2 °C | 11.6 °C – 12.8 °C | cold |
| December | 10.8 °C | 10.4 °C – 11.2 °C | cold |
Compared with August, the water cools down by 0.8 °C in September. The warmest month: August (15.8 °C). The coldest: February (9.4 °C).
Nearby, in September
- United Kingdom 14.3 °C · cool
- Netherlands 17.7 °C · cool
- France 20.1 °C · warm
- Denmark 16.3 °C · cool
- Germany 17.0 °C · cool
- Portugal 20.2 °C · pleasant
And right now?
For the temperature measured right now, station by station and to the hour: Ireland: water temperature
Frequently asked questions
What is the sea temperature in September?
Ireland, in September: 15.0 °C on average along the coast, from 14.2 °C in the coolest waters to 15.7 °C in the warmest (average of the years 2011 to 2025).
Can you swim in September?
Where the water is warmest (15.7 °C), it is cool. Swimming is fine if you like cool water: you get used to it after a few minutes, especially in mild weather.
What is the best month for swimming?
The water is warmest in August (15.8 °C on average) and coldest in February (9.4 °C). Even where it is warmest, the water never reaches 20 °C in any month; the three warmest months are: August, July, September.
Where is the water warmest in September?
The warmest in September: United Kingdom (14.3 °C), Netherlands (17.7 °C), France (20.1 °C). The coolest: Portugal (20.2 °C).
Where do these temperatures come from?
These are averages of the sea surface temperature from 2011 to 2025, computed from NOAA satellite images (OISST, one value about every 50 km), in a 100 km strip along the coasts of the main country: distant territories (overseas, remote islands) are not counted. It is an estimate, not a measurement taken at the beach: lakes and rivers are not included.