Swimming in Northern Ireland in september 2025 Sea temperature by city in september
Do you want to go to the beach in Northern Ireland in september 2025? Is it the right month to go for pleasant temperatures and staying in the water for a long time? The answer is on this page with the sea temperatures in september in Northern Ireland by city and our opinion on the chances of enjoying pleasant sea conditions.
Sea temperature in Northern Ireland in september 2025
Here, find the average sea temperature in Northern Ireland in september in several coastal cities.
County Antrim in september
58°F
min: 57°F / max: 59°F
Ballycastle (Causeway Coast)
58°F
min: 56°F / max: 59°F
Larne
58°F
min: 57°F / max: 59°F
Carrickfergus
58°F
min: 57°F / max: 59°F
Glenariff
58°F
min: 57°F / max: 59°F
Newtownabbey
58°F
min: 57°F / max: 59°F
County Londonderry in september
58°F
min: 57°F / max: 60°F
Castlerock
58°F
min: 57°F / max: 60°F
Limavady
58°F
min: 56°F / max: 60°F
58°F
min: 56°F / max: 59°F
County Down in september
Donwpatrick
59°F
min: 58°F / max: 60°F
Annalong
59°F
min: 58°F / max: 60°F
Ballywalter
58°F
min: 57°F / max: 59°F
Bangor
58°F
min: 57°F / max: 59°F
Donaghadee
58°F
min: 57°F / max: 59°F
Dundrum
59°F
min: 58°F / max: 60°F
Where should you go swimming in Northern Ireland in the month of september?
Swimming in Northern Ireland in september is freezing
In september in Northern Ireland swimming conditions are generally the same everywhere.
Forget about swimming in Belfast, Ballycastle (Causeway Coast), Derry (Londonderry), Donwpatrick, Larne, Annalong, Ballywalter, Bangor, Carrickfergus, Castlerock, Donaghadee, Dundrum, Glenariff, Holywood, Kilkeel, Limavady, Millisle, Newcastle, Newtownabbey, Newtownards, Portrush, Portstewart and Warrenpoint in september! The water temperature is freezing, reaching as low as 57°F (and only 59°F at the best of times). Our advice: plan on sightseeing, and don't bring your beach towel!
Where to go swimming in Northern Ireland in september: the map of sea temperatures
ideal swimming 
pleasant swimming 
cool swimming 
cold swimming 
freezing swimmingWater temperature and seasonal norms in september
Belfast
| September | |||
| Average sea temperature | 58°F | ||
| Minimum sea temperature | 57°F | ||
| Maximum sea temperature | 59°F | ||
| Average outside temperature | 58°F | ||
| Maximum outside temperature | 61°F | ||
| Minimum outside temperature | 52°F | ||
| Precipitation | 3.9in | ||
| Number of days of precipitation | 6 jour(s) (20%) | ||
| Cloud cover | 57% | ||
| Our opinion | freezing swimming |
More information on swimming in Belfast in september
Ballycastle (Causeway Coast)
| September | |||
| Average sea temperature | 58°F | ||
| Minimum sea temperature | 56°F | ||
| Maximum sea temperature | 59°F | ||
| Average outside temperature | 58°F | ||
| Maximum outside temperature | 59°F | ||
| Minimum outside temperature | 54°F | ||
| Precipitation | 5.2in | ||
| Number of days of precipitation | 9 jour(s) (31%) | ||
| Cloud cover | 57% | ||
| Our opinion | freezing swimming |
Derry (Londonderry)
| September | |||
| Average sea temperature | 58°F | ||
| Minimum sea temperature | 57°F | ||
| Maximum sea temperature | 60°F | ||
| Average outside temperature | 56°F | ||
| Maximum outside temperature | 61°F | ||
| Minimum outside temperature | 50°F | ||
| Precipitation | 1.7in | ||
| Number of days of precipitation | 1 jour(s) (5%) | ||
| Cloud cover | 65% | ||
| Our opinion | freezing swimming |
More information on swimming in Derry (Londonderry) in september
Donwpatrick
| September | |||
| Average sea temperature | 59°F | ||
| Minimum sea temperature | 58°F | ||
| Maximum sea temperature | 60°F | ||
| Average outside temperature | 58°F | ||
| Maximum outside temperature | 61°F | ||
| Minimum outside temperature | 56°F | ||
| Precipitation | 3in | ||
| Number of days of precipitation | 5 jour(s) (15%) | ||
| Cloud cover | 51% | ||
| Our opinion | freezing swimming |
Larne
| September | |||
| Average sea temperature | 58°F | ||
| Minimum sea temperature | 57°F | ||
| Maximum sea temperature | 59°F | ||
| Average outside temperature | 58°F | ||
| Maximum outside temperature | 61°F | ||
| Minimum outside temperature | 54°F | ||
| Precipitation | 4.1in | ||
| Number of days of precipitation | 7 jour(s) (22%) | ||
| Cloud cover | 55% | ||
| Our opinion | freezing swimming |
List of coastal cities in Northern Ireland
| Belfast in september | freezing swimming |
| Ballycastle (Causeway Coast) in september | freezing swimming |
| Derry (Londonderry) in september | freezing swimming |
| Donwpatrick in september | freezing swimming |
| Larne in september | freezing swimming |
| Annalong in september | freezing swimming |
| Ballywalter in september | freezing swimming |
| Bangor in september | freezing swimming |
| Carrickfergus in september | freezing swimming |
| Castlerock in september | freezing swimming |
| Donaghadee in september | freezing swimming |
| Dundrum in september | freezing swimming |
| Glenariff in september | freezing swimming |
| Holywood in september | freezing swimming |
| Kilkeel in september | freezing swimming |
| Limavady in september | freezing swimming |
| Millisle in september | freezing swimming |
| Newcastle in september | freezing swimming |
| Newtownabbey in september | freezing swimming |
| Newtownards in september | freezing swimming |
| Portrush in september | freezing swimming |
| Portstewart in september | freezing swimming |
| Warrenpoint in september | freezing swimming |