Jacksonville weather in September

In September, Jacksonville sees average daytime highs of 78°F and overnight lows near 58°F, with 2.9 in of rain across 7.5 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 9th-wettest month of the year here.

Highs ease over the month, from about 82°F in the first days to 74°F by the end. The sky is clear or mostly clear about 49% 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 Jacksonville's 1st-clearest and 10th-windiest month. For the whole year in context, see Jacksonville's year-round climate.

Daytime high
78°
4th warmest
Overnight low
58°
9th coldest
Rainfall
2.9 in
7.5 wet days
Daylight
12 h 18 min
5:48 AM – 6:03 PM
Cloud cover
45%
1st clearest
Wind
7 mph
10th windiest
Solar energy
4.75 kWh/m²
Travel score
7.3
out of 10

Jacksonville is city in Morgan County, Illinois, United States.

Density
691/km²
people per km²
Founded
1825

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 82°F in the first days to 74°F by the end.

A typical September day in Jacksonville reaches about 78°F in the afternoon and slips back to 58°F overnight — a 20°F spread between the day's warmth and the night's chill. On most days the high lands between 68°F and 88°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)
18363
28363
38263
48262
58262
68162
78161
88161
98060
108060
118060
127959
137959
147958
157858
167858
177857
187757
197756
207756
217656
227655
237655
247554
257554
267454
277453
287453
297352
307352

How September really feels in Jacksonville

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.

Jacksonville 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 (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan36° / 21°2.37.749.50.0
Feb41° / 24°2.27.23.410.40.3
Mar52° / 34°3.110.31.611.72.8
Apr64° / 45°4.611.50.4135.4
May74° / 55°4.413.4014.26.2
Jun82° / 65°4.111.1014.85.8
Jul85° / 68°3.39.5014.55.3
Aug84° / 66°3.09013.65.7
Sep78° / 58°2.97.5012.37.3
Oct66° / 46°3.08.30.110.96.3
Nov52° / 35°3.28.20.99.82.8
Dec40° / 26°2.37.42.79.20.2

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 49% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 13% of September, with mostly cloudy or overcast conditions the remaining 38%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16337
26436
36436
46436
56436
66436
76436
86436
96337
106337
116238
126238
136139
146040
156040
165941
175941
185941
195941
205941
216040
226040
236139
246139
256238
266238
276337
286337
296337
306238

Chance of precipitation in September

Any precipitation

Jacksonville gets around 2.9 in of rain over 7.5 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 25% and peaks near 27% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
126
225
325
425
525
625
725
825
925
1026
1126
1226
1326
1426
1526
1627
1726
1826
1926
2026
2126
2225
2325
2425
2524
2624
2724
2824
2923
3023

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 43% of days. Sticky, muggy-or-worse air turns up on roughly 20% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
11620242713
21820242612
32021242511
42121232410
5232223239
6252223228
7272322217
8292322206
9312321196
10332321185
11352320184
12372320174
13382319163
14402219163
15422218153
16442118152
17462117152
18482116141
19502016141
20512015131
21541914121
22561814120
23581813110
24591713110
25611712100
2663161290
2764161190
2865161180
2967151080
3068151070

Wind in September

Winds average 7 mph in September.

Across September, daily wind ranges from about 6 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
16calm
26calm
36calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247calm
257calm
267calm
277light breeze
288light breeze
298light breeze
308light breeze

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 5:33 AM to 6:01 AM, and sunset from 6:28 PM to 5:39 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:336:28
212.95:346:26
312.85:356:25
412.85:366:23
512.75:376:22
612.75:386:20
712.75:396:18
812.65:406:17
912.65:416:15
1012.55:426:13
1112.55:436:11
1212.45:446:10
1312.45:456:08
1412.35:466:06
1512.35:476:05
1612.35:486:03
1712.25:486:01
1812.25:496:00
1912.15:505:58
2012.15:515:56
2112.05:525:54
2212.05:535:53
2311.95:545:51
2411.95:555:49
2511.95:565:48
2611.85:575:46
2711.85:585:44
2811.75:595:43
2911.76:005:41
3011.66:015:39

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.75 kWh/m².

For context, solar energy here swings from a low near 1.84 kWh/m² to a high of 6.46 kWh/m² in June across the year — September's 4.75 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.3Bright
25.2Bright
35.2Bright
45.2Bright
55.1Bright
65.1Bright
75.0Bright
85.0Bright
95.0Bright
104.9Bright
114.9Bright
124.8Bright
134.8Bright
144.8Bright
154.7Bright
164.7Bright
174.6Bright
184.6Bright
194.6Bright
204.5Bright
214.5Bright
224.5Bright
234.4Bright
244.4Bright
254.4Bright
264.3Bright
274.3Bright
284.2Bright
294.2Bright
304.2Bright
Planning a trip in September

Is September a good time to visit Jacksonville?

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

7.3
Sightseeing
1st-best month of the year
6.7
Beach & pool
3rd-best month of the year

September is one of the better times to visit Jacksonville for general sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Jacksonville in September

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

In September, Jacksonville sees daytime highs around 78°F and nights near 58°F. Worth packing: light clothes and sun protection. About 8 days see rain.

light clothessun protection

UV index in Jacksonville 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 Jacksonville peaks around June 21 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 10 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highModerateJun 21UV 9Dec 22UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep7High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Jacksonville 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 Jacksonville is worst in July — around 16 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (October, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodModerateGoodJul 1716 µg/m³Oct 238 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb13Moderate
Mar12Moderate
Apr11Good
May14Moderate
Jun14Moderate
Jul16Moderate
Aug14Moderate
Sep11Good
Oct8Good
Nov8Good
Dec9Good
Location & terrain

Where is Jacksonville?

Jacksonville sits at 39.7°N, 90.2°W, 610 ft above sea level, in United States. The nearest listed city is Springfield, 32 mi away.

Topography around Jacksonville

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

Within 2 miles, the terrain around Jacksonville has only modest variations in elevation — a maximum elevation change of 177 ft around an average of 604 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 243 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 604 ft.

The land around Jacksonville is covered by trees (32%), grassland (25%) and cropland (23%) within 2 miles, cropland (74%) within 10 miles, and cropland (65%) and trees (27%) within 50 miles.

2 miles
177 ft
10 miles
243 ft
50 miles
604 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Springfield 32 mi · Godfrey 54 mi · Macomb 55 mi · Upper Alton 57 mi · Alton 58 mi · Hannibal 60 mi · Old Jamestown 62 mi · Quincy 64 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 Jacksonville (39.7339°, -90.229°, elevation 610 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).