Duncan weather in September

In September, Duncan sees average daytime highs of 85°F and overnight lows near 65°F, with 2.8 in of rain across 6.4 wet days and about 12.2 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 90°F in the first days to 82°F by the end. The sky is clear or mostly clear about 57% of the time in September, and the air most often feels muggy.

Daylight stretches from about 12 h 48 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Duncan's 3rd-clearest and 11th-windiest month. For the whole year in context, see Duncan's year-round climate.

Daytime high
85°
4th warmest
Overnight low
65°
9th coldest
Rainfall
2.8 in
6.4 wet days
Daylight
12 h 12 min
6:20 AM – 6:33 PM
Cloud cover
39%
3rd clearest
Wind
7 mph
11th windiest
Solar energy
5.16 kWh/m²
Travel score
5.8
out of 10

Duncan is city and county seat of Stephens County, Oklahoma, United States.

Density
188/km²
people per km²
Founded
1892

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 90°F in the first days to 82°F by the end.

A typical September day in Duncan reaches about 85°F in the afternoon and slips back to 65°F overnight — a 20°F spread between the day's warmth and the night's chill. On most days the high lands between 75°F and 95°F. Set against its neighbours, September runs about 8°F cooler than August and about 11°F warmer than October.

40°60°80°100°151015202530
Avg high (°F)Avg low (°F)
19171
29070
39070
48970
58969
68969
78869
88868
98768
108768
118767
128667
138667
148666
158566
168565
178565
188465
198464
208464
218464
228363
238363
248362
258362
268262
278261
288261
298160
308160

How September really feels in Duncan

Once humidity and wind are folded in, September averages 5 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
5
heat index over the day's high
Days feeling ≤ 32°F
0
wind chill below the day's low

The story in September is heat — humidity pushes the afternoon "feels like" well above the raw temperature.

Duncan 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 (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan52° / 32°1.54.80.9103.2
Feb56° / 36°1.85.80.910.74.4
Mar65° / 44°3.17.60.411.76.4
Apr73° / 52°3.67.9012.87.3
May81° / 62°4.710.6013.86.3
Jun89° / 70°3.68.6014.34.4
Jul94° / 74°1.85.8014.13.2
Aug93° / 73°1.95.6013.33.4
Sep85° / 65°2.86.4012.25.8
Oct74° / 54°3.56.8011.17.6
Nov62° / 42°2.15.50.210.26.2
Dec53° / 34°2.05.20.89.73.5

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 57% 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 28%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
17624
27525
37525
47426
57327
67327
77228
87129
97030
107030
117030
126832
136832
146832
156733
166733
176832
186832
196832
206931
217030
227228
237228
247426
257426
267525
277525
287624
297624
307624

Chance of precipitation in September

Any precipitation

Duncan gets around 2.8 in of rain over 6.4 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 22% and peaks near 25% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
120
220
321
421
522
623
723
823
924
1024
1124
1225
1325
1425
1525
1625
1724
1824
1923
2023
2122
2221
2320
2419
2518
2618
2718
2818
2918
3018

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the muggy band about 29% of days. Sticky, muggy-or-worse air turns up on roughly 35% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
181729388
291828388
3101828378
4111827368
5121827358
6131827358
7141726348
8151726348
9161725348
10171625348
11181624348
12191624348
13201524337
14211523337
15231523337
16241523326
17251523326
18271522315
19291522305
20311522285
21331522274
22351521254
23371521243
24391621223
25411620212
26421720192
27441719182
28461719162
29471819152
30481818142

Wind in September

Winds average 7 mph in September.

Across September, daily wind ranges from about 7 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (mph)Feels
17calm
27calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147light breeze
158light breeze
168light breeze
178light breeze
188light breeze
198light breeze
208light breeze
218light breeze
228light breeze
238light breeze
248light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 48 min at the start of September to 11 h 42 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 66 minutes over September. Sunrise moves from 6:09 AM to 6:30 AM, and sunset from 6:54 PM to 6:12 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.86:096:54
212.76:106:53
312.76:106:51
412.76:116:50
512.66:126:49
612.66:126:47
712.56:136:46
812.56:146:44
912.56:156:43
1012.46:156:41
1112.46:166:40
1212.46:176:38
1312.36:186:37
1412.36:186:35
1512.26:196:34
1612.26:206:33
1712.26:216:31
1812.16:216:30
1912.16:226:28
2012.16:236:27
2112.06:236:25
2212.06:246:24
2312.06:256:22
2411.96:266:21
2511.96:266:19
2611.86:276:18
2711.86:286:16
2811.86:296:15
2911.76:306:13
3011.76:306:12

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.16 kWh/m².

For context, solar energy here swings from a low near 2.59 kWh/m² to a high of 6.94 kWh/m² in July across the year — September's 5.16 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.8Bright
25.7Bright
35.7Bright
45.6Bright
55.5Bright
65.5Bright
75.5Bright
85.4Bright
95.3Bright
105.3Bright
115.3Bright
125.2Bright
135.2Bright
145.1Bright
155.1Bright
165.1Bright
175.0Bright
185.0Bright
195.0Bright
205.0Bright
215.0Bright
225.0Bright
235.0Bright
244.9Bright
254.9Bright
264.9Bright
274.9Bright
284.8Bright
294.8Bright
304.8Bright
Planning a trip in September

Is September a good time to visit Duncan?

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

5.8
Sightseeing
6th-best month of the year
7.6
Beach & pool
1st-best month of the year

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

What to pack for Duncan in September

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

In September, Duncan sees daytime highs around 85°F and nights near 65°F. Pack light clothes. Worth having: sun protection. About 6 days see rain.

light clothessun protection

UV index in Duncan in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 7 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Duncan peaks around June 23 at about 10 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 21 at about 3 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 11 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highExtremeVery highHighModerateJun 23UV 10Dec 21UV 3
UV index (midday)Level
Jan3Moderate
Feb5Moderate
Mar6High
Apr9Very high
May9Very high
Jun10Extreme
Jul10Extreme
Aug10Very high
Sep7Very high
Oct6High
Nov4Moderate
Dec3Moderate
Location & terrain

Where is Duncan?

Duncan sits at 34.5°N, 98.0°W, 1,122 ft above sea level, in United States. The nearest listed city is Lawton, 25 mi away.

Topography around Duncan

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

Within 2 miles, the terrain around Duncan has only modest variations in elevation — a maximum elevation change of 167 ft around an average of 1,125 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 367 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,716 ft.

The land around Duncan is covered by grassland (39%), trees (29%) and artificial surfaces (27%) within 2 miles, grassland (64%) and trees (25%) within 10 miles, and grassland (66%) within 50 miles.

2 miles
167 ft
10 miles
367 ft
50 miles
1,716 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Lawton 25 mi · Chickasha 38 mi · Wichita Falls 51 mi · Ardmore 52 mi · Norman 58 mi · Mustang 62 mi · Moore 64 mi · Yukon 70 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 Duncan (34.5023°, -97.9578°, elevation 1,122 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. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).