Belfast weather in September

In September, Belfast sees average daytime highs of 16°C and overnight lows near 11°C, with 70 mm of rain across 12.5 wet days and about 12.5 hours of daylight. It is the 4th-warmest and 9th-wettest month of the year here.

Highs ease over the month, from about 17°C in the first days to 15°C by the end. The sky is clear or mostly clear about 8% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 h 36 min at the start of September to 11 h 24 min by month's end. Set against the rest of the year, September is Belfast's 9th-clearest and 8th-windiest month. For the whole year in context, see Belfast's year-round climate.

Daytime high
16°
4th warmest
Overnight low
11°
10th coldest
Rainfall
70 mm
12.5 wet days
Daylight
12 h 24 min
6:05 AM – 6:31 PM
Cloud cover
77%
9th clearest
Wind
15 km/h
8th windiest
Solar energy
2.69 kWh/m²
Travel score
4.4
out of 10

Belfast is capital city of Northern Ireland.

Air quality
Moderate
PM2.5 10.6 µg/m³ · 2019
Density
3,026/km²
people per km²

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 17°C in the first days to 15°C by the end.

A typical September day in Belfast reaches about 16°C in the afternoon and slips back to 11°C overnight — a 5°C spread between the day's warmth and the night's chill. On most days the high lands between 13°C and 18°C. Set against its neighbours, September runs about 2°C cooler than August and about 3°C warmer than October.

10°15°20°151015202530
Avg high (°C)Avg low (°C)
11712
21712
31711
41711
51711
61711
71611
81611
91611
101611
111611
121611
131611
141611
151611
161611
171611
181610
191510
201510
211510
221510
231510
241510
251510
261510
271510
281510
291510
301410

How September really feels in Belfast

Once humidity and wind are folded in, September averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Belfast weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 9th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 7714.20.87.61.0
Feb / 6212.10.99.31.1
Mar / 6213.40.611.51.6
Apr11° / 65130.213.72.5
May14° / 7014.10.115.83.5
Jun16° / 11°7513.2016.94.4
Jul18° / 12°8114.6016.44.9
Aug18° / 12°8114.2014.74.9
Sep16° / 11°7012.5012.54.4
Oct13° / 8713.5010.23.1
Nov10° / 85140.28.21.9
Dec / 8213.50.57.11.2

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 8% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 15% of September, with mostly cloudy or overcast conditions the remaining 78%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
12179
22278
32278
42179
52179
62179
72179
82278
92278
102278
112278
122278
132278
142476
152476
162476
172377
182377
192377
202377
212377
222377
232377
242377
252377
262377
272476
282377
292377
302377

Chance of precipitation in September

Any precipitation

Belfast gets around 70 mm of rain over 12.5 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 42% and peaks near 45% on the wettest days.

0%20%40%60%151015202530
Rain chance (%)
140
240
340
441
541
641
742
842
942
1042
1142
1242
1342
1442
1541
1641
1740
1840
1940
2040
2140
2240
2341
2441
2542
2643
2743
2844
2945
3045

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the dry band about 86% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)
180191
280191
380191
481181
581181
681181
782171
882171
983161
1084151
1184151
1285141
1386131
1486131
1586131
1688120
1788120
1888120
1988120
2088120
2189110
2289110
2389110
2489110
2589110
2690100
2790100
2890100
299190
309190

Wind in September

Winds average 15 km/h in September.

Across September, daily wind ranges from about 15 km/h on the calmest days to 16 km/h at its breeziest. It stays fairly steady from day to day.

05101520151015202530
Wind speed (km/h)Feels
115light breeze
215light breeze
315light breeze
415light breeze
515light breeze
615light breeze
715light breeze
815light breeze
915light breeze
1015light breeze
1115light breeze
1215light breeze
1315light breeze
1415light breeze
1515light breeze
1615light breeze
1715light breeze
1815light breeze
1915light breeze
2016light breeze
2116light breeze
2216light breeze
2316light breeze
2416light breeze
2516light breeze
2616light breeze
2716light breeze
2816light breeze
2916light breeze
3016light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 h 36 min at the start of September to 11 h 24 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 132 minutes over September. Sunrise moves from 5:37 AM to 6:32 AM, and sunset from 7:10 PM to 5:54 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.65:377:10
213.55:397:08
313.45:407:05
413.35:427:02
513.35:447:00
613.25:466:57
713.15:486:55
813.05:506:52
913.05:526:49
1012.95:546:47
1112.85:566:44
1212.75:576:42
1312.75:596:39
1412.66:016:36
1512.56:036:34
1612.46:056:31
1712.46:076:28
1812.36:096:26
1912.26:116:23
2012.16:136:21
2112.16:146:18
2212.06:166:15
2311.96:186:13
2411.86:206:10
2511.86:226:07
2611.76:246:05
2711.66:266:02
2811.56:285:59
2911.56:305:57
3011.46:325:54

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 2.69 kWh/m².

For context, solar energy here swings from a low near 0.47 kWh/m² to a high of 4.95 kWh/m² in May across the year — September's 2.69 kWh/m² falls in the middle.

01234151015202530
Solar energy (kWh/m²)Level
13.2Moderate
23.2Moderate
33.2Moderate
43.1Moderate
53.1Moderate
63.0Moderate
73.0Moderate
83.0Moderate
92.9Moderate
102.9Moderate
112.9Moderate
122.8Moderate
132.8Moderate
142.8Moderate
152.7Moderate
162.7Moderate
172.7Moderate
182.6Moderate
192.6Moderate
202.5Moderate
212.5Moderate
222.5Moderate
232.4Moderate
242.4Moderate
252.3Moderate
262.3Moderate
272.2Moderate
282.2Moderate
292.2Moderate
302.1Moderate
Planning a trip in September

Is September a good time to visit Belfast?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

4.4
Sightseeing
3rd-best month of the year
0.5
Beach & pool
4th-best month of the year

September is a reasonable time to visit Belfast for sightseeing.

What to pack for Belfast in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Belfast sees daytime highs around 16°C and nights near 11°C. Worth packing: a warm layer and rain gear. About 13 days see rain.

a warm layerrain gear

Sea temperature near Belfast in September

The nearest coast averages about 14°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 31 km away) is warmest in September at about 14°C and coldest in March near 8°C.

The water stays below 20°C all year — cool enough that most swimmers want a wetsuit.

6°8°10°12°14°16°JanFebMarAprMayJunJulAugSepOctNovDecbracingcool
Sea temperature (°C)Comfort
Jan9Bracing
Feb8Bracing
Mar8Bracing
Apr8Bracing
May9Bracing
Jun11Bracing
Jul12Bracing
Aug13Bracing
Sep14Bracing
Oct14Bracing
Nov12Bracing
Dec11Bracing

UV index in Belfast in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 3 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Belfast peaks around July 24 at about 5 (high) — a little sun protection helps at midday. It bottoms out near January 1 at about 0 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 5 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighModerateLowJul 24UV 5Jan 1UV 0
UV index (midday)Level
Jan0Low
Feb1Low
Mar2Moderate
Apr3Moderate
May5High
Jun5High
Jul5High
Aug5High
Sep3Moderate
Oct2Low
Nov1Low
Dec0Low
Location & terrain

Where is Belfast?

Belfast sits at 54.6°N, 5.9°W, 7 m above sea level, in United Kingdom. The nearest listed city is Castlereagh, 4.0 km away.

Topography around Belfast

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Belfast.

Within 3 km, the terrain around Belfast has only modest variations in elevation — a maximum elevation change of 76 m around an average of 15 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 495 m; within 80 km, large variations in elevation — a maximum elevation change of 860 m.

The land around Belfast is covered by artificial surfaces (72%) within 3 km, grassland (58%) within 16 km, and grassland (47%) and water (45%) within 80 km.

3 km
76 m
16 km
495 m
80 km
860 m
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Castlereagh 4.0 km · Newtownabbey 7.0 km · Lisburn 11 km · Newtownards 15 km · Carrickfergus 15 km · Bangor 18 km · Antrim 23 km · Larne 29 km

United Kingdom travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type D / G / M
230 V · 50 Hz
Prices
≈ 89% of US
price level, 2025
GDP per capita
$57,602
2025
Happiness
6.7 / 10
World Happiness, 2025
Safe drinking water
100%
of population, 2024
Homicide rate
1.1
per 100k, 2021
Road deaths
3.2
per 100k/yr, 2019
Income group
High
World Bank
Religion
Christian 60%none 26%Muslim 4%other 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Belfast (54.5968°, -5.9254°, elevation 7 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).