Grande-Synthe weather in September

In September, Grande-Synthe sees average daytime highs of 19°C and overnight lows near 13°C, with 55 mm of rain across 9.8 wet days and about 12.4 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 20°C in the first days to 17°C by the end. The sky is clear or mostly clear about 18% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 h 24 min at the start of September to 11 h 30 min by month's end. Set against the rest of the year, September is Grande-Synthe's 6th-clearest and 9th-windiest month. For the whole year in context, see Grande-Synthe's year-round climate.

Daytime high
19°
4th warmest
Overnight low
13°
10th coldest
Rainfall
55 mm
9.8 wet days
Daylight
12 h 24 min
6:34 AM – 6:57 PM
Cloud cover
66%
6th clearest
Wind
15 km/h
9th windiest
Solar energy
3.24 kWh/m²
Travel score
5.9
out of 10
Air quality
Good
PM10 23.4 µg/m³ · 2019

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 20°C in the first days to 17°C by the end.

A typical September day in Grande-Synthe reaches about 19°C in the afternoon and slips back to 13°C overnight — a 6°C spread between the day's warmth and the night's chill. On most days the high lands between 16°C and 23°C. Set against its neighbours, September runs about 3°C cooler than August and about 4°C warmer than October.

10°15°20°25°151015202530
Avg high (°C)Avg low (°C)
12014
22014
32014
42014
52013
62013
72013
82013
92013
101913
111913
121913
131913
141913
151913
161913
171912
181912
191912
201812
211812
221812
231812
241812
251812
261812
271812
281712
291711
301711

How September really feels in Grande-Synthe

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.

Grande-Synthe weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 5611.80.98.20.9
Feb / 47100.89.61.1
Mar10° / 4610.60.511.52.3
Apr13° / 4410.20.113.53.7
May16° / 10°5410.7015.35.1
Jun19° / 12°549.9016.26.0
Jul22° / 15°5410.5015.86.5
Aug22° / 15°6310.5014.36.5
Sep19° / 13°559.8012.45.9
Oct15° / 10°6511.9010.44.2
Nov11° / 6512.80.38.72.3
Dec / 6812.50.87.81.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 18% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 19% of September, with mostly cloudy or overcast conditions the remaining 63%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
13862
23862
33763
43763
53763
63763
73763
83763
93565
103565
113565
123664
133664
143664
153664
163664
173664
183763
193763
203763
213763
223862
233862
243862
253862
263763
273565
283565
293565
303367

Chance of precipitation in September

Any precipitation

Grande-Synthe gets around 55 mm of rain over 9.8 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 34% and peaks near 39% on the wettest days. The odds climb toward the end of the month.

0%10%20%30%40%50%151015202530
Rain chance (%)
129
229
329
429
529
629
730
830
931
1032
1132
1233
1333
1433
1534
1634
1735
1835
1935
2035
2136
2236
2336
2436
2537
2637
2738
2838
2938
3039

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 64% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)
15036131
25235130
35335120
45434120
55533120
65632120
75632120
85731120
95930110
105930110
116129100
126129100
13632890
14642880
15652780
16662770
17682660
18682660
19692650
20702640
21702640
22702730
23702730
24712720
25712720
26712720
27722710
28722710
29732610
30742510

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
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 24 min at the start of September to 11 h 30 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 114 minutes over September. Sunrise moves from 6:10 AM to 6:57 AM, and sunset from 7:32 PM to 6:24 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.46:107:32
213.36:117:29
313.26:137:27
413.26:147:25
513.16:167:22
613.06:187:20
713.06:197:18
812.96:217:15
912.86:227:13
1012.86:247:11
1112.76:267:08
1212.66:277:06
1312.66:297:04
1412.56:307:01
1512.46:326:59
1612.46:346:57
1712.36:356:54
1812.26:376:52
1912.26:396:49
2012.16:406:47
2112.06:426:45
2212.06:436:42
2311.96:456:40
2411.96:476:38
2511.86:486:35
2611.76:506:33
2711.76:526:31
2811.66:536:28
2911.56:556:26
3011.56:576:24

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 3.24 kWh/m².

For context, solar energy here swings from a low near 0.66 kWh/m² to a high of 5.63 kWh/m² in June across the year — September's 3.24 kWh/m² falls in the middle.

01234151015202530
Solar energy (kWh/m²)Level
13.9Moderate
23.8Moderate
33.8Moderate
43.7Moderate
53.7Moderate
63.6Moderate
73.6Moderate
83.6Moderate
93.5Moderate
103.5Moderate
113.4Moderate
123.4Moderate
133.3Moderate
143.3Moderate
153.3Moderate
163.2Moderate
173.2Moderate
183.1Moderate
193.1Moderate
203.0Moderate
213.0Moderate
222.9Moderate
232.9Moderate
242.8Moderate
252.8Moderate
262.7Moderate
272.7Moderate
282.6Moderate
292.6Moderate
302.5Moderate
Planning a trip in September

Is September a good time to visit Grande-Synthe?

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

5.9
Sightseeing
4th-best month of the year
2.5
Beach & pool
4th-best month of the year

September is a reasonable time to visit Grande-Synthe for sightseeing.

What to pack for Grande-Synthe in September

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

In September, Grande-Synthe sees daytime highs around 19°C and nights near 13°C. Worth packing: rain gear. About 10 days see rain.

rain gear

Sea temperature near Grande-Synthe in September

The nearest coast averages about 18°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 13 km away) is warmest in August at about 18°C and coldest in February near 7°C.

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

5°10°15°20°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshing
Sea temperature (°C)Comfort
Jan8Bracing
Feb7Bracing
Mar7Bracing
Apr9Bracing
May12Bracing
Jun15Bracing
Jul17Cool
Aug18Cool
Sep18Cool
Oct15Cool
Nov13Bracing
Dec10Bracing

UV index in Grande-Synthe in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 4 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Grande-Synthe peaks around June 22 at about 6 (high) — sunscreen and a hat are worth it in the middle of the day. It bottoms out near January 1 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 6 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighModerateLowJun 22UV 6Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb1Low
Mar3Moderate
Apr4Moderate
May6High
Jun6High
Jul6High
Aug6High
Sep4Moderate
Oct2Moderate
Nov1Low
Dec1Low
Location & terrain

Where is Grande-Synthe?

Grande-Synthe sits at 51.0°N, 2.3°E, 2 m above sea level, in France. The nearest listed city is Saint-Pol-sur-Mer, 3.0 km away.

Topography around Grande-Synthe

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

Within 3 km, the terrain around Grande-Synthe has only modest variations in elevation — a maximum elevation change of 42 m around an average of 5 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 52 m; within 80 km, significant variations in elevation — a maximum elevation change of 290 m.

The land around Grande-Synthe is covered by artificial surfaces (50%) and trees (22%) within 3 km, water (39%) and cropland (37%) within 16 km, and water (38%) and cropland (34%) within 80 km.

3 km
42 m
16 km
52 m
80 km
290 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Saint-Pol-sur-Mer 3.0 km · Dunkirk 6.0 km · Coudekerque-Branche 7.0 km · Koksijde 26 km · Saint-Omer 30 km · Calais 32 km · Poperinge 35 km · Hazebrouck 36 km

France travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type C / E
230 V · 50 Hz
Prices
≈ 77% of US
price level, 2025
GDP per capita
$48,986
2025
Happiness
6.6 / 10
World Happiness, 2025
Safe drinking water
100%
of population, 2024
Homicide rate
1.3
per 100k, 2023
Road deaths
5.1
per 100k/yr, 2019
Income group
High
World Bank
English
Moderate
EF EPI 539
Religion
Roman Catholic 47%none 33%Muslim 4%Protestant 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 Grande-Synthe (51.0154°, 2.2997°, elevation 2 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).