Wilmington weather in September

In September, Wilmington sees average daytime highs of 77°F and overnight lows near 61°F, with 4.2 in of rain across 9.6 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 1st-wettest month of the year here.

Highs ease over the month, from about 81°F in the first days to 73°F by the end. The sky is clear or mostly clear about 37% of the time in September, and the air most often feels dry.

Daylight stretches from about 12 h 54 min at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Wilmington's 2nd-clearest and 9th-windiest month. For the whole year in context, see Wilmington's year-round climate.

Daytime high
77°
4th warmest
Overnight low
61°
9th coldest
Rainfall
4.2 in
9.6 wet days
Daylight
12 h 18 min
5:49 AM – 6:04 PM
Cloud cover
55%
2nd clearest
Wind
6 mph
9th windiest
Solar energy
4.29 kWh/m²
Travel score
6.9
out of 10

Wilmington is seat of New Castle County, and largest city in Delaware, United States.

Density
1,615/km²
people per km²
Founded
1638

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 81°F in the first days to 73°F by the end.

A typical September day in Wilmington reaches about 77°F in the afternoon and slips back to 61°F overnight — a 16°F spread between the day's warmth and the night's chill. On most days the high lands between 69°F and 85°F. Set against its neighbours, September runs about 6°F cooler than August and about 11°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18266
28166
38165
48165
58165
68065
78064
88064
98064
107963
117963
127863
137862
147862
157762
167761
177761
187660
197660
207660
217559
227559
237559
247458
257458
267458
277357
287357
297356
307256

How September really feels in Wilmington

Once humidity and wind are folded in, September averages 0 days that feel above 90°F and 0 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
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.

Wilmington weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 1st-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan41° / 28°3.29.23.69.50.1
Feb43° / 29°3.08.73.210.40.6
Mar52° / 36°4.110.72.111.72.7
Apr63° / 46°3.610.50.3135.4
May73° / 55°3.510.9014.26.5
Jun81° / 65°3.910.4014.86.0
Jul86° / 70°3.910.9014.55.0
Aug83° / 68°3.910.4013.65.6
Sep77° / 61°4.29.6012.36.9
Oct66° / 50°3.68.1010.96.3
Nov55° / 40°3.07.90.29.83.6
Dec45° / 33°3.991.99.21.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 37% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 47%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15446
25446
35446
45446
55446
65347
75446
85446
95446
105446
115446
125446
135446
145446
155347
165347
175248
185149
195149
205149
215050
225050
235149
245149
255248
265248
275248
285248
295347
305446

Chance of precipitation in September

Any precipitation

Wilmington gets around 4.2 in of rain over 9.6 wet days in September, the wettest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 30% and peaks near 33% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
128
228
329
429
529
629
729
830
930
1029
1129
1229
1329
1429
1529
1629
1730
1830
1931
2031
2132
2232
2333
2433
2533
2633
2733
2833
2932
3032

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 34% of days. Sticky, muggy-or-worse air turns up on roughly 26% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
11618252416
21719242416
31819242415
41919242315
52019232214
62219232214
72319232113
82420232113
92519232012
102719232011
112819231911
122919231910
13311923199
14321922188
15331922187
16351922177
17361922176
18372021175
19382021165
20392021164
21402020164
22422019163
23432019153
24442118152
25462117152
26472017142
27482016142
28502015141
29512015131
30531914131

Wind in September

Winds average 6 mph in September.

Across September, daily wind ranges from about 6 mph on the calmest days to 6 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
16calm
26calm
36calm
46calm
56calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
306calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 54 min at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 78 minutes over September. Sunrise moves from 5:34 AM to 6:03 AM, and sunset from 6:29 PM to 5:40 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:346:29
212.95:356:28
312.85:366:26
412.85:376:24
512.75:386:23
612.75:396:21
712.75:406:19
812.65:416:18
912.65:426:16
1012.55:436:14
1112.55:446:13
1212.45:456:11
1312.45:466:09
1412.35:476:08
1512.35:486:06
1612.35:496:04
1712.25:506:03
1812.25:516:01
1912.15:525:59
2012.15:535:57
2112.05:545:56
2212.05:555:54
2311.95:565:52
2411.95:575:51
2511.95:585:49
2611.85:595:47
2711.86:005:45
2811.76:015:44
2911.76:025:42
3011.66:035:40

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.29 kWh/m².

For context, solar energy here swings from a low near 1.85 kWh/m² to a high of 6.11 kWh/m² in June across the year — September's 4.29 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.9Bright
24.8Bright
34.8Bright
44.8Bright
54.7Bright
64.7Bright
74.6Bright
84.6Bright
94.6Bright
104.5Bright
114.5Bright
124.5Bright
134.4Bright
144.4Bright
154.3Bright
164.3Bright
174.3Bright
184.2Bright
194.2Bright
204.1Bright
214.1Bright
224.0Bright
234.0Bright
244.0Moderate
253.9Moderate
263.9Moderate
273.9Moderate
283.8Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Hazard calendar for Wilmington

In seasonPeak

In September, Wilmington sits inside its atlantic hurricane season. The full year is below, with each hazard's peak months called out.

Wilmington sits in the Atlantic hurricane belt; the season peaks August–October.

Atlantic hurricane
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is September a good time to visit Wilmington?

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

6.9
Sightseeing
1st-best month of the year
6.2
Beach & pool
4th-best month of the year

September is a reasonable time to visit Wilmington for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Wilmington in September

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

In September, Wilmington sees daytime highs around 77°F and nights near 61°F. Worth packing: light clothes and rain gear. About 10 days see rain.

light clothesrain gear

UV index in Wilmington in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Wilmington peaks around July 11 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 at about 2 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateLowJul 11UV 8Dec 20UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May8Very high
Jun8Very high
Jul9Very high
Aug6High
Sep6High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Wilmington in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Wilmington is worst in July — around 17 µg/m³ PM2.5 (moderate), about 2.0× the cleanest month (November, 8 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1317 µg/m³Nov 128 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb12Good
Mar13Moderate
Apr13Moderate
May15Moderate
Jun16Moderate
Jul17Moderate
Aug14Moderate
Sep12Good
Oct9Good
Nov8Good
Dec9Good
Location & terrain

Where is Wilmington?

Wilmington sits at 39.7°N, 75.5°W, 92 ft above sea level, in United States. The nearest listed city is Bear, 9.9 mi away.

Topography around Wilmington

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Wilmington.

Within 2 miles, the terrain around Wilmington has only modest variations in elevation — a maximum elevation change of 364 ft around an average of 82 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 545 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,483 ft.

The land around Wilmington is covered by artificial surfaces (47%) and trees (32%) within 2 miles, trees (51%) within 10 miles, and trees (53%) within 50 miles.

2 miles
364 ft
10 miles
545 ft
50 miles
1,483 ft
treesgrasslandcroplandartificial surfacesbare terrainwaterwetland
September weather nearby: Bear 9.9 mi · Newark 12 mi · Chester 12 mi · West Chester 15 mi · Springfield 17 mi · Elkton 18 mi · Drexel Hill 19 mi · Havertown 21 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 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 Wilmington (39.746°, -75.5466°, elevation 92 ft), 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. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).