Londonderry County Borough weather in September

In September, Londonderry County Borough sees average daytime highs of 16°C and overnight lows near 10°C, with 75 mm of rain across 14.2 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 16°C in the first days to 14°C by the end. The sky is clear or mostly clear about 4% 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 Londonderry County Borough's 9th-clearest and 8th-windiest month. For the whole year in context, see Londonderry County Borough's year-round climate.

Daytime high
16°
4th warmest
Overnight low
10°
10th coldest
Rainfall
75 mm
14.2 wet days
Daylight
12 h 24 min
6:10 AM – 6:37 PM
Cloud cover
80%
9th clearest
Wind
15 km/h
8th windiest
Solar energy
2.55 kWh/m²
Travel score
4.1
out of 10

Londonderry County Borough is city in Northern Ireland.

Density
225/km²
people per km²
Founded
~501 CE

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 16°C in the first days to 14°C by the end.

A typical September day in Londonderry County Borough reaches about 16°C in the afternoon and slips back to 10°C overnight — a 6°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)
11711
21711
31711
41611
51611
61611
71611
81611
91610
101610
111610
121610
131610
141610
151610
161610
171510
181510
191510
201510
21159
22159
23159
24159
25159
26159
27159
28149
29149
30149

How September really feels in Londonderry County Borough

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.

Londonderry County Borough 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 / 8716.427.50.8
Feb / 7514.91.99.31.0
Mar / 7515.61.211.41.6
Apr11° / 7415.40.313.82.4
May14° / 7815.10.115.83.4
Jun16° / 10°8715.50174.1
Jul17° / 12°9316.8016.54.5
Aug17° / 12°9416.7014.74.5
Sep16° / 10°7514.2012.54.1
Oct13° / 8815.50.110.22.9
Nov10° / 9016.70.38.11.6
Dec / 9015.81.271.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 4% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 13% of September, with mostly cloudy or overcast conditions the remaining 83%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
11684
21684
31684
41684
51585
61585
71585
81585
91585
101684
111684
121684
131783
141783
151783
161783
171882
181882
191882
201882
211981
221981
231981
242080
251981
261981
271981
281981
292080
302080

Chance of precipitation in September

Any precipitation

Londonderry County Borough gets around 75 mm of rain over 14.2 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 47% and peaks near 50% on the wettest days.

0%20%40%60%151015202530
Rain chance (%)
148
248
348
449
549
650
750
850
950
1050
1150
1250
1350
1449
1548
1647
1747
1846
1945
2045
2144
2244
2344
2445
2545
2646
2746
2847
2947
3047

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 88% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)
182171
282171
383161
483161
583161
684151
784151
884151
985141
1086131
1186131
1287121
1387121
1488111
1589110
1689110
1790100
1890100
1990100
2090100
2190100
2290100
239190
249190
259190
269190
279190
289280
299280
309370

Wind in September

Winds average 15 km/h in September.

Across September, daily wind ranges from about 14 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
114light 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
2015light breeze
2115light breeze
2215light breeze
2315light breeze
2415light breeze
2515light breeze
2615light 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 5:41 AM to 6:38 AM, and sunset from 7:16 PM to 6:00 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.65:417:16
213.55:437:14
313.45:457:11
413.45:477:09
513.35:497:06
613.25:517:03
713.15:537:01
813.15:556:58
913.05:576:55
1012.95:596:53
1112.86:016:50
1212.76:036:47
1312.76:056:45
1412.66:066:42
1512.56:086:39
1612.46:106:37
1712.46:126:34
1812.36:146:31
1912.26:166:29
2012.16:186:26
2112.16:206:23
2212.06:226:21
2311.96:246:18
2411.86:266:15
2511.86:286:13
2611.76:306:10
2711.66:326:07
2811.56:346:05
2911.46:366:02
3011.46:386:00

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 2.55 kWh/m².

For context, solar energy here swings from a low near 0.42 kWh/m² to a high of 4.84 kWh/m² in May across the year — September's 2.55 kWh/m² falls in the middle.

01234151015202530
Solar energy (kWh/m²)Level
13.1Moderate
23.0Moderate
33.0Moderate
43.0Moderate
52.9Moderate
62.9Moderate
72.9Moderate
82.8Moderate
92.8Moderate
102.8Moderate
112.7Moderate
122.7Moderate
132.6Moderate
142.6Moderate
152.6Moderate
162.6Moderate
172.5Moderate
182.5Moderate
192.5Moderate
202.4Moderate
212.4Moderate
222.3Moderate
232.3Moderate
242.3Moderate
252.2Moderate
262.2Moderate
272.1Moderate
282.1Moderate
292.0Moderate
302.0Moderate
Planning a trip in September

Is September a good time to visit Londonderry County Borough?

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

4.1
Sightseeing
3rd-best month of the year
Beach & pool
never really warm enough

September is a reasonable time to visit Londonderry County Borough for sightseeing.

What to pack for Londonderry County Borough in September

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

In September, Londonderry County Borough sees daytime highs around 16°C and nights near 10°C. Pack rain gear. Worth having: a warm layer. About 14 days see rain.

rain geara warm layer

Sea temperature near Londonderry County Borough 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 42 km away) is warmest in August at about 15°C and coldest in February near 8°C.

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

10°15°JanFebMarAprMayJunJulAugSepOctNovDecbracingcool
Sea temperature (°C)Comfort
Jan9Bracing
Feb8Bracing
Mar8Bracing
Apr9Bracing
May10Bracing
Jun12Bracing
Jul14Bracing
Aug15Bracing
Sep14Bracing
Oct13Bracing
Nov12Bracing
Dec10Bracing

UV index in Londonderry County Borough 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 Londonderry County Borough peaks around July 13 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 6 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighModerateLowJul 13UV 5Jan 1UV 0
UV index (midday)Level
Jan0Low
Feb1Low
Mar2Moderate
Apr3Moderate
May5High
Jun5Moderate
Jul5High
Aug5Moderate
Sep3Moderate
Oct2Low
Nov1Low
Dec0Low
Location & terrain

Where is Londonderry County Borough?

Londonderry County Borough sits at 55.0°N, 7.3°W, 24 m above sea level, in United Kingdom. The nearest listed city is Derry, 0.0 km away.

BallymenaAntrimPortadownCraigavon

Topography around Londonderry County Borough

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

Within 3 km, the terrain around Londonderry County Borough has only modest variations in elevation — a maximum elevation change of 192 m around an average of 47 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 481 m; within 80 km, large variations in elevation — a maximum elevation change of 706 m.

The land around Londonderry County Borough is covered by artificial surfaces (31%), grassland (30%) and trees (27%) within 3 km, grassland (65%) within 16 km, and grassland (57%) and water (34%) within 80 km.

3 km
192 m
16 km
481 m
80 km
706 m
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Derry 0.0 km · Letterkenny 28 km · Coleraine 44 km · Omagh 44 km · Ballymena 68 km · Antrim 77 km · Portadown 85 km · Craigavon 85 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 Londonderry County Borough (54.9972°, -7.3092°, elevation 24 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).