Smithtown weather in September

In September, Smithtown sees average daytime highs of 71°F and overnight lows near 64°F, with 3.8 in of rain across 9.1 wet days and about 12.3 hours of daylight. It is the 3rd-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 74°F in the first days to 68°F by the end. The sky is clear or mostly clear about 42% 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 Smithtown's 3rd-clearest and 8th-windiest month. For the whole year in context, see Smithtown's year-round climate.

Daytime high
71°
3rd warmest
Overnight low
64°
10th coldest
Rainfall
3.8 in
9.1 wet days
Daylight
12 h 18 min
5:39 AM – 5:55 PM
Cloud cover
53%
3rd clearest
Wind
10 mph
8th windiest
Solar energy
4.43 kWh/m²
Travel score
6.9
out of 10

Smithtown is town in Suffolk County, New York, United States.

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 74°F in the first days to 68°F by the end.

A typical September day in Smithtown reaches about 71°F in the afternoon and slips back to 64°F overnight — a 7°F spread between the day's warmth and the night's chill. On most days the high lands between 66°F and 76°F. Set against its neighbours, September runs about 5°F cooler than August and about 9°F warmer than October.

50°60°70°80°151015202530
Avg high (°F)Avg low (°F)
17568
27568
37468
47468
57467
67467
77467
87367
97366
107366
117366
127266
137265
147265
157265
167164
177164
187164
197164
207063
217063
227063
236962
246962
256962
266961
276861
286861
296760
306760

How September really feels in Smithtown

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.

Smithtown weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan39° / 30°3.89.949.40.0
Feb39° / 30°3.59.33.710.40.0
Mar44° / 35°4.610.62.911.70.8
Apr53° / 44°3.810.90.413.12.8
May61° / 54°3.510.8014.25.0
Jun71° / 64°3.69.9014.96.6
Jul77° / 71°3.39.4014.67.0
Aug77° / 70°3.99.5013.67.1
Sep71° / 64°3.89.1012.36.9
Oct62° / 55°4.49.2010.95.5
Nov53° / 44°3.78.90.39.73.0
Dec44° / 36°4.810.62.39.10.9

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 42% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 13% of September, with mostly cloudy or overcast conditions the remaining 45%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15941
25842
35743
45743
55743
65743
75743
85644
95644
105644
115644
125545
135545
145545
155446
165446
175446
185347
195248
205248
215248
225149
235248
245248
255248
265347
275347
285347
295446
305446

Chance of precipitation in September

Any precipitation

Smithtown gets around 3.8 in of rain over 9.1 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 32% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
126
226
326
427
527
627
728
828
928
1028
1128
1228
1328
1429
1529
1629
1729
1829
1930
2030
2131
2231
2332
2432
2532
2632
2732
2832
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 26% of days. Sticky, muggy-or-worse air turns up on roughly 29% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1820263115
2920263014
31020263014
41120262913
51320262913
61420262812
71520262811
81620262810
9172026279
10192025279
11202025278
12212025267
13232025266
14242125255
15262125254
16272124244
17282124233
18302124223
19312124222
20322224212
21332224202
22342223191
23362322181
24372322171
25392321161
26402321151
27422320151
28432319141
29452319130
30462318120

Wind in September

Winds average 10 mph in September.

Across September, daily wind ranges from about 9 mph on the calmest days to 11 mph at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (mph)Feels
19light breeze
29light breeze
39light breeze
49light breeze
59light breeze
69light breeze
710light breeze
810light breeze
910light breeze
1010light breeze
1110light breeze
1210light breeze
1310light breeze
1410light breeze
1510light breeze
1610light breeze
1710light breeze
1810light breeze
1910light breeze
2010light breeze
2110light breeze
2210light breeze
2310light breeze
2410light breeze
2510light breeze
2610light breeze
2710light breeze
2810light breeze
2910light breeze
3011light breeze

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 5:54 AM, and sunset from 6:21 PM to 5:31 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:246:21
212.95:256:19
312.95:266:18
412.85:276:16
512.85:286:14
612.75:296:13
712.75:306:11
812.65:316:09
912.65:326:07
1012.55:336:06
1112.55:346:04
1212.55:356:02
1312.45:366:00
1412.45:375:59
1512.35:385:57
1612.35:395:55
1712.25:405:53
1812.25:415:52
1912.15:425:50
2012.15:435:48
2112.05:445:46
2212.05:455:45
2311.95:465:43
2411.95:475:41
2511.85:485:39
2611.85:495:38
2711.85:505:36
2811.75:525:34
2911.75:535:32
3011.65:545:31

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.43 kWh/m².

For context, solar energy here swings from a low near 1.76 kWh/m² to a high of 6.38 kWh/m² in June across the year — September's 4.43 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.1Bright
25.0Bright
35.0Bright
45.0Bright
54.9Bright
64.9Bright
74.8Bright
84.8Bright
94.7Bright
104.7Bright
114.7Bright
124.6Bright
134.6Bright
144.5Bright
154.5Bright
164.4Bright
174.4Bright
184.3Bright
194.3Bright
204.3Bright
214.2Bright
224.2Bright
234.1Bright
244.1Bright
254.0Bright
264.0Moderate
273.9Moderate
283.9Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Hazard calendar for Smithtown

In seasonPeak

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

Smithtown 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 Smithtown?

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

6.9
Sightseeing
3rd-best month of the year
4.7
Beach & pool
3rd-best month of the year

September is a reasonable time to visit Smithtown for sightseeing.

What to pack for Smithtown in September

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

In September, Smithtown sees daytime highs around 71°F and nights near 64°F. Worth packing: rain gear. About 9 days see rain.

rain gear

Sea temperature near Smithtown in September

The nearest coast averages about 70°F in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 16 mi away) is warmest in August at about 73°F and coldest in February near 40°F.

It's comfortable for a long swim from Jul 3 to Sep 23 — about 2.7 months when the water holds above 68°F.

40°50°60°70°80°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmcomfortable to swim
Sea temperature (°F)Comfort
Jan43Bracing
Feb40Bracing
Mar40Bracing
Apr45Bracing
May54Bracing
Jun64Cool
Jul72Refreshing
Aug73Refreshing
Sep70Refreshing
Oct63Cool
Nov55Bracing
Dec49Bracing

UV index in Smithtown 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 Smithtown 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 22 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 22UV 1
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May7Very high
Jun8Very high
Jul8Very high
Aug6High
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Smithtown 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 Smithtown is worst in July — around 19 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (November, 9 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1018 µg/m³Nov 169 µg/m³
PM2.5 (µg/m³)Level
Jan11Good
Feb13Moderate
Mar15Moderate
Apr16Moderate
May18Moderate
Jun18Moderate
Jul19Moderate
Aug16Moderate
Sep13Moderate
Oct10Good
Nov9Good
Dec10Good
Location & terrain

Where is Smithtown?

Smithtown sits at 40.9°N, 73.2°W, 59 ft above sea level, in United States. The nearest listed city is Hauppauge, 1.9 mi away.

Topography around Smithtown

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

Within 2 miles, the terrain around Smithtown has only modest variations in elevation — a maximum elevation change of 203 ft around an average of 89 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 361 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,526 ft.

The land around Smithtown is covered by trees (80%) within 2 miles, trees (56%) and water (20%) within 10 miles, and water (49%) and trees (38%) within 50 miles.

2 miles
203 ft
10 miles
361 ft
50 miles
1,526 ft
treesgrasslandartificial surfaceswaterwetland
September weather nearby: Hauppauge 1.9 mi · Kings Park 3.7 mi · Ronkonkoma 3.7 mi · Lake Ronkonkoma 3.7 mi · Central Islip 4.3 mi · Commack 5.0 mi · Centereach 5.6 mi · Brentwood 5.6 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 Smithtown (40.8559°, -73.2007°, elevation 59 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).