Delaware weather in September

In September, Delaware sees average daytime highs of 75°F and overnight lows near 56°F, with 2.9 in of rain across 8.8 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 11th-wettest month of the year here.

Highs ease over the month, from about 79°F in the first days to 71°F by the end. The sky is clear or mostly clear about 39% 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 Delaware's 1st-clearest and 10th-windiest month. For the whole year in context, see Delaware's year-round climate.

Daytime high
75°
4th warmest
Overnight low
56°
9th coldest
Rainfall
2.9 in
8.8 wet days
Daylight
12 h 18 min
6:19 AM – 6:34 PM
Cloud cover
51%
1st clearest
Wind
7 mph
10th windiest
Solar energy
4.47 kWh/m²
Travel score
7.1
out of 10

Delaware is city in Ohio, United States; county seat of Delaware County.

Density
769/km²
people per km²
Founded
1808

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 79°F in the first days to 71°F by the end.

A typical September day in Delaware reaches about 75°F in the afternoon and slips back to 56°F overnight — a 19°F spread between the day's warmth and the night's chill. On most days the high lands between 65°F and 85°F. Set against its neighbours, September runs about 6°F cooler than August and about 12°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18061
28061
37961
47960
57960
67860
77859
87859
97859
107758
117758
127758
137657
147657
157656
167556
177556
187555
197455
207455
217454
227354
237353
247353
257253
267252
277152
287151
297151
307051

How September really feels in Delaware

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.

Delaware weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 11th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan35° / 22°3.311.169.50.0
Feb39° / 24°2.79.24.610.40.0
Mar49° / 32°3.811.32.811.71.9
Apr62° / 42°4.512.70.8134.8
May71° / 53°4.413.5014.26.0
Jun80° / 62°4.111.9014.86.2
Jul83° / 65°3.611.4014.65.9
Aug81° / 64°2.99.6013.66.6
Sep75° / 56°2.98.8012.37.1
Oct63° / 45°2.99.20.210.95.6
Nov50° / 35°3.29.61.29.82.3
Dec40° / 27°3.410.23.99.20.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 39% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 17% of September, with mostly cloudy or overcast conditions the remaining 44%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15842
25842
35842
45842
55842
65842
75842
85842
95743
105743
115743
125644
135644
145644
155545
165545
175545
185545
195446
205446
215347
225347
235446
245446
255446
265446
275446
285347
295347
305347

Chance of precipitation in September

Any precipitation

Delaware gets around 2.9 in of rain over 8.8 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 29% and peaks near 30% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
129
229
329
429
529
629
729
829
928
1028
1128
1228
1328
1428
1529
1629
1729
1829
1929
2029
2129
2230
2330
2430
2530
2630
2730
2830
2930
3030

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 48% of days. Sticky, muggy-or-worse air turns up on roughly 14% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1252521255
2262520245
3272520234
4292619224
5302619214
6322618203
7342718193
8362717183
9372717172
10392717162
11402716151
12422616141
13442616141
14452615131
15472515121
16492515110
17512414110
18532314100
1955231390
2057221380
2158211380
2261201270
2362191270
2464191160
2565181160
2667171060
2768171050
2869161050
2969161050
307215940

Wind in September

Winds average 7 mph in September.

Across September, daily wind ranges from about 6 mph on the calmest days to 7 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
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247calm
257calm
267calm
277calm
287calm
297calm
307calm

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 6:04 AM to 6:33 AM, and sunset from 7:00 PM to 6:10 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.96:047:00
212.96:056:58
312.86:066:57
412.86:076:55
512.86:086:53
612.76:096:52
712.76:106:50
812.66:116:48
912.66:126:47
1012.56:136:45
1112.56:146:43
1212.46:156:41
1312.46:166:40
1412.46:176:38
1512.36:186:36
1612.36:196:34
1712.26:206:33
1812.26:216:31
1912.16:226:29
2012.16:236:28
2112.06:246:26
2212.06:256:24
2311.96:266:22
2411.96:276:21
2511.96:286:19
2611.86:296:17
2711.86:306:15
2811.76:316:14
2911.76:326:12
3011.66:336:10

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.47 kWh/m².

For context, solar energy here swings from a low near 1.6 kWh/m² to a high of 6.22 kWh/m² in June across the year — September's 4.47 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.0Bright
25.0Bright
35.0Bright
44.9Bright
54.9Bright
64.8Bright
74.8Bright
84.8Bright
94.7Bright
104.7Bright
114.7Bright
124.6Bright
134.6Bright
144.6Bright
154.5Bright
164.5Bright
174.4Bright
184.4Bright
194.3Bright
204.3Bright
214.3Bright
224.2Bright
234.2Bright
244.1Bright
254.1Bright
264.0Bright
274.0Moderate
283.9Moderate
293.9Moderate
303.9Moderate
Planning a trip in September

Is September a good time to visit Delaware?

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

7.1
Sightseeing
1st-best month of the year
5.9
Beach & pool
4th-best month of the year

September is one of the better times to visit Delaware for general sightseeing.

What to pack for Delaware in September

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

In September, Delaware sees daytime highs around 75°F and nights near 56°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Delaware 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 Delaware peaks around June 20 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 at about 2 (low).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJun 20UV 9Dec 22UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May8Very high
Jun10Very high
Jul9Very high
Aug8Very high
Sep6High
Oct3Moderate
Nov3Moderate
Dec2Low

Air quality in Delaware 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 Delaware is worst in July — around 17 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (October, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1216 µg/m³Oct 238 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb12Good
Mar12Moderate
Apr12Moderate
May15Moderate
Jun16Moderate
Jul17Moderate
Aug15Moderate
Sep12Good
Oct8Good
Nov8Good
Dec9Good
Location & terrain

Where is Delaware?

Delaware sits at 40.3°N, 83.1°W, 869 ft above sea level, in United States. The nearest listed city is Westerville, 14 mi away.

Topography around Delaware

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

Within 2 miles, the terrain around Delaware has only modest variations in elevation — a maximum elevation change of 194 ft around an average of 922 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 315 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,033 ft.

The land around Delaware is covered by trees (43%), artificial surfaces (23%) and grassland (20%) within 2 miles, cropland (43%), trees (29%) and grassland (21%) within 10 miles, and cropland (56%) and trees (26%) within 50 miles.

2 miles
194 ft
10 miles
315 ft
50 miles
1,033 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Westerville 14 mi · Dublin 14 mi · Marysville 16 mi · Hilliard 19 mi · Marion 21 mi · Upper Arlington 21 mi · Gahanna 22 mi · Columbus 24 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 Delaware (40.2987°, -83.068°, elevation 869 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. 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).