Norwalk weather in September

In September, Norwalk sees average daytime highs of 73°F and overnight lows near 62°F, with 3.7 in of rain across 9 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 77°F in the first days to 69°F by the end. The sky is clear or mostly clear about 38% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Norwalk's 2nd-clearest and 9th-windiest month. For the whole year in context, see Norwalk's year-round climate.

Daytime high
73°
4th warmest
Overnight low
62°
9th coldest
Rainfall
3.7 in
9 wet days
Daylight
12 h 18 min
5:40 AM – 5:56 PM
Cloud cover
55%
2nd clearest
Wind
7 mph
9th windiest
Solar energy
4.27 kWh/m²
Travel score
7.0
out of 10

Norwalk is city in Fairfield County, Connecticut, United States.

Density
940/km²
people per km²
Founded
1640

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 77°F in the first days to 69°F by the end.

A typical September day in Norwalk reaches about 73°F in the afternoon and slips back to 62°F overnight — a 12°F spread between the day's warmth and the night's chill. On most days the high lands between 66°F and 80°F. Set against its neighbours, September runs about 7°F cooler than August and about 11°F warmer than October.

40°50°60°70°80°151015202530
Avg high (°F)Avg low (°F)
17866
27766
37766
47765
57765
67665
77665
87664
97664
107564
117563
127563
137463
147462
157462
167362
177361
187361
197261
207260
217260
227160
237159
247159
257059
267058
276958
286958
296957
306857

How September really feels in Norwalk

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.

Norwalk 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
Jan37° / 26°3.394.69.40.0
Feb39° / 27°3.18.6410.40.0
Mar46° / 34°4.110.33.411.71.2
Apr57° / 44°3.610.50.413.13.9
May67° / 54°3.410.9014.35.9
Jun76° / 64°3.710.8014.96.6
Jul82° / 70°3.610.8014.76.3
Aug80° / 69°4.110.5013.66.5
Sep73° / 62°3.79012.37.0
Oct62° / 51°4.08.5010.95.6
Nov52° / 41°3.28.50.49.72.9
Dec43° / 33°4.19.82.79.10.5

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 38% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 14% of September, with mostly cloudy or overcast conditions the remaining 48%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15446
25446
35446
45347
55347
65347
75347
85446
95446
105446
115446
125347
135347
145446
155347
165347
175248
185248
195149
205149
215050
225050
235050
245050
255050
265050
275149
285149
295149
305248

Chance of precipitation in September

Any precipitation

Norwalk gets around 3.7 in of rain over 9 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 (%)
128
228
328
428
528
628
728
828
929
1029
1129
1229
1329
1429
1529
1629
1729
1829
1929
2029
2129
2229
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 32% of days. Sticky, muggy-or-worse air turns up on roughly 24% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
11323272512
21423272512
31523262412
41623262411
51723262311
61823252310
72023252210
8212325229
9222324229
10242324218
11252324217
12272323217
13282323206
14292323205
15312222195
16322222194
17342222184
18352222183
19362221173
20382221172
21392221162
22402320152
23422319152
24432319141
25442318131
26462318121
27472318121
28492317111
29502317101
30512216101

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
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
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 13 hours 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 84 minutes over September. Sunrise moves from 5:24 AM to 5:55 AM, and sunset from 6:22 PM to 5:31 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:246:22
212.95:256:21
312.95:276:19
412.85:286:17
512.85:296:15
612.75:306:14
712.75:316:12
812.65:326:10
912.65:336:08
1012.55:346:07
1112.55:356:05
1212.55:366:03
1312.45:376:01
1412.45:386:00
1512.35:395:58
1612.35:405:56
1712.25:415:54
1812.25:425:52
1912.15:435:51
2012.15:445:49
2112.05:455:47
2212.05:465:45
2311.95:475:44
2411.95:485:42
2511.85:495:40
2611.85:505:38
2711.85:515:37
2811.75:525:35
2911.75:535:33
3011.65:555:31

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.27 kWh/m².

For context, solar energy here swings from a low near 1.73 kWh/m² to a high of 6.1 kWh/m² in June across the year — September's 4.27 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
94.5Bright
104.5Bright
114.5Bright
124.4Bright
134.4Bright
144.3Bright
154.3Bright
164.3Bright
174.2Bright
184.2Bright
194.1Bright
204.1Bright
214.1Bright
224.0Bright
234.0Moderate
243.9Moderate
253.9Moderate
263.8Moderate
273.8Moderate
283.7Moderate
293.7Moderate
303.7Moderate
Planning a trip in September

Hazard calendar for Norwalk

In seasonPeak

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

Norwalk 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 Norwalk?

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

7.0
Sightseeing
1st-best month of the year
5.3
Beach & pool
4th-best month of the year

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

What to pack for Norwalk in September

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

In September, Norwalk sees daytime highs around 73°F and nights near 62°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

Sea temperature near Norwalk in September

The nearest coast averages about 71°F in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea offshore is warmest in August at about 74°F and coldest in February near 35°F.

It's comfortable for a long swim from Jun 30 to Sep 30 — about 3.1 months when the water holds above 68°F.

30°40°50°60°70°80°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°F)Comfort
Jan39Bracing
Feb35Bracing
Mar37Bracing
Apr44Bracing
May55Bracing
Jun65Cool
Jul72Refreshing
Aug74Refreshing
Sep71Refreshing
Oct64Cool
Nov55Bracing
Dec46Bracing

UV index in Norwalk 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 Norwalk peaks around July 11 at about 8 (very high) — sunscreen and a hat are worth it in the middle of the day. It bottoms out near December 23 at about 1 (low).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 11UV 8Dec 23UV 1
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May7Very high
Jun8Very high
Jul8Very high
Aug6High
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Norwalk 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 Norwalk is worst in July — around 20 µg/m³ PM2.5 (moderate), about 1.7× the cleanest month (November, 11 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateJul 1220 µg/m³Nov 1612 µg/m³
PM2.5 (µg/m³)Level
Jan13Moderate
Feb16Moderate
Mar17Moderate
Apr17Moderate
May18Moderate
Jun19Moderate
Jul20Moderate
Aug17Moderate
Sep16Moderate
Oct13Moderate
Nov11Good
Dec13Moderate
Location & terrain

Where is Norwalk?

Norwalk sits at 41.1°N, 73.4°W, 36 ft above sea level, in United States. The nearest listed city is East Norwalk, 1.2 mi away.

Topography around Norwalk

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

Within 2 miles, the terrain around Norwalk has only modest variations in elevation — a maximum elevation change of 253 ft around an average of 85 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 781 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,913 ft.

The land around Norwalk is covered by trees (56%) and artificial surfaces (26%) within 2 miles, trees (54%) and water (36%) within 10 miles, and trees (55%) and water (30%) within 50 miles.

2 miles
253 ft
10 miles
781 ft
50 miles
1,913 ft
treesgrasslandartificial surfaceswaterwetland
September weather nearby: East Norwalk 1.2 mi · Westport 3.1 mi · Darien 4.3 mi · New Canaan 5.0 mi · Wilton 5.6 mi · North Stamford 7.5 mi · Fairfield 7.5 mi · Stamford 8.1 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 Norwalk (41.1176°, -73.4079°, elevation 36 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). 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. 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).