Key West weather in September

In September, Key West sees average daytime highs of 83°F and overnight lows near 80°F, with 5.4 in of rain across 17.7 wet days and about 12.2 hours of daylight. It is the 3rd-warmest and 1st-wettest month of the year here.

Day-to-day highs hold fairly steady near 83°F through the month. The sky is clear or mostly clear about 31% of the time in September, and the air most often feels miserable.

Daylight stretches from about 12 h 30 min at the start of September to 11 h 48 min by month's end. Set against the rest of the year, September is Key West's 12th-clearest and 9th-windiest month. For the whole year in context, see Key West's year-round climate.

Daytime high
83°
3rd warmest
Overnight low
80°
10th coldest
Rainfall
5.4 in
17.7 wet days
Daylight
12 h 06 min
6:17 AM – 6:26 PM
Cloud cover
61%
12th clearest
Wind
11 mph
9th windiest
Solar energy
5.49 kWh/m²
Travel score
4.7
out of 10

Key West is county seat of Monroe County, Florida, United States.

Density
1,373/km²
people per km²
Founded
1828

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 83°F through the month.

A typical September day in Key West reaches about 83°F in the afternoon and slips back to 80°F overnight — a 3°F spread between the day's warmth and the night's chill. On most days the high lands between 82°F and 85°F. Set against its neighbours, September runs on par with August and about 2°F warmer than October.

75°80°85°151015202530
Avg high (°F)Avg low (°F)
18481
28481
38481
48481
58481
68481
78481
88381
98380
108380
118380
128380
138380
148380
158380
168380
178380
188380
198380
208380
218380
228380
238380
248380
258380
268380
278380
288380
298380
308280

How September really feels in Key West

Once humidity and wind are folded in, September averages 28 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
28
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.

Key West weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 1st-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysDaylight (hours)Travel score
Jan73° / 69°1.55.710.67.8
Feb73° / 70°1.2411.18.1
Mar74° / 71°1.04.211.88.4
Apr77° / 74°1.54.512.68.3
May80° / 77°2.67.913.27.3
Jun83° / 80°4.112.713.55.7
Jul84° / 81°2.512.913.45.3
Aug84° / 81°4.116.112.94.8
Sep83° / 80°5.417.712.24.7
Oct81° / 78°4.612.711.46.2
Nov77° / 74°1.55.810.87.8
Dec75° / 71°1.35.110.58.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 31% of the time in September, the cloudiest month of the year.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 52%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
14654
24555
34555
44555
54555
64555
74654
84555
94654
104753
114753
124852
134852
144951
154951
164951
174951
185050
194951
205050
215050
225050
235050
244951
254951
264951
274951
284951
294951
304951

Chance of precipitation in September

Any precipitation

Key West gets around 5.4 in of rain over 17.7 wet days in September, the wettest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 59% and peaks near 63% on the wettest days.

0%20%40%60%151015202530
Rain chance (%)
163
263
363
462
562
662
761
861
960
1060
1159
1258
1358
1457
1557
1657
1756
1856
1957
2057
2157
2257
2358
2458
2558
2659
2759
2858
2958
3057

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the miserable band about 54% of days. Sticky, muggy-or-worse air turns up on roughly 100% of them.

0%25%50%75%100%151015202530
Muggy (%)Oppressive (%)Miserable (%)
103268
203367
303466
403565
503664
603763
703862
803862
903961
1004060
1104159
1204258
1304357
1414455
1514455
1614554
1714653
1814752
1914851
2014950
2115049
2215148
2325246
2425345
2525444
2635344
2735443
2845442
2945541
3055441

Wind in September

Winds average 11 mph in September.

Across September, daily wind ranges from about 11 mph on the calmest days to 12 mph at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (mph)Feels
111light breeze
211light breeze
311light breeze
411light breeze
511light breeze
611light breeze
711light breeze
811light breeze
911light breeze
1011light breeze
1111light breeze
1211light breeze
1311light breeze
1411light breeze
1511light breeze
1611light breeze
1711light breeze
1811light breeze
1911light breeze
2011light breeze
2111light breeze
2211light breeze
2311light breeze
2411light breeze
2512light breeze
2612light breeze
2712light breeze
2812light breeze
2912light breeze
3012light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 30 min at the start of September to 11 h 48 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 42 minutes over September. Sunrise moves from 6:12 AM to 6:23 AM, and sunset from 6:42 PM to 6:10 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.56:126:42
212.56:126:41
312.56:126:40
412.46:136:39
512.46:136:38
612.46:146:37
712.46:146:36
812.36:146:34
912.36:156:33
1012.36:156:32
1112.36:156:31
1212.26:166:30
1312.26:166:29
1412.26:166:28
1512.26:176:27
1612.16:176:26
1712.16:186:25
1812.16:186:23
1912.16:186:22
2012.06:196:21
2112.06:196:20
2212.06:196:19
2312.06:206:18
2411.96:206:17
2511.96:216:16
2611.96:216:15
2711.96:216:14
2811.86:226:13
2911.86:226:11
3011.86:236:10

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.49 kWh/m².

For context, solar energy here swings from a low near 3.66 kWh/m² to a high of 6.9 kWh/m² in May across the year — September's 5.49 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.9Bright
25.9Bright
35.8Bright
45.8Bright
55.8Bright
65.8Bright
75.7Bright
85.7Bright
95.7Bright
105.6Bright
115.6Bright
125.6Bright
135.5Bright
145.5Bright
155.5Bright
165.5Bright
175.5Bright
185.4Bright
195.4Bright
205.4Bright
215.3Bright
225.3Bright
235.3Bright
245.2Bright
255.2Bright
265.2Bright
275.2Bright
285.1Bright
295.1Bright
305.1Bright
Planning a trip in September

Hazard calendar for Key West

In seasonPeak

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

Key West sits in the Atlantic hurricane belt; the season peaks August–October.

Key West's rainy season runs May–October, when most of the year's rain falls.

Atlantic hurricane
Rainy season
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is September a good time to visit Key West?

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

4.7
Sightseeing
12th-best month of the year
5.7
Beach & pool
12th-best month of the year

September is a reasonable time to visit Key West for sightseeing.

What to pack for Key West in September

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

In September, Key West sees daytime highs around 83°F and nights near 80°F. Pack light clothes and rain gear. Worth having: sun protection. About 18 days see rain.

light clothesrain gearsun protection

Sea temperature near Key West in September

The nearest coast averages about 85°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 86°F and coldest in February near 73°F.

The water stays above 68°F all year — warm enough for a swim any month.

70°75°80°85°90°JanFebMarAprMayJunJulAugSepOctNovDecrefreshingwarmtropicalcomfortable to swim
Sea temperature (°F)Comfort
Jan73Refreshing
Feb73Refreshing
Mar74Refreshing
Apr77Warm
May80Warm
Jun83Tropical
Jul85Tropical
Aug86Tropical
Sep85Tropical
Oct83Tropical
Nov78Warm
Dec75Warm

UV index in Key West in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 11 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Key West peaks around July 18 at about 12 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 18 at about 5 (high).

The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecHighVery highExtremeVery highHighJul 18UV 12Dec 18UV 5
UV index (midday)Level
Jan6High
Feb8Very high
Mar10Very high
Apr11Extreme
May11Extreme
Jun11Extreme
Jul12Extreme
Aug12Extreme
Sep11Extreme
Oct9Very high
Nov6High
Dec5High

Air quality in Key West 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 Key West is worst in July — around 18 µg/m³ PM2.5 (moderate), about 4.1× the cleanest month (December, 4 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1818 µg/m³Dec 144 µg/m³
PM2.5 (µg/m³)Level
Jan5Good
Feb5Good
Mar6Good
Apr8Good
May9Good
Jun15Moderate
Jul18Moderate
Aug16Moderate
Sep10Good
Oct7Good
Nov5Good
Dec4Good
Location & terrain

Where is Key West?

Key West sits at 24.6°N, 81.8°W, 3 ft above sea level, in United States. The nearest listed city is Marco Island, 96 mi away.

Topography around Key West

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

Within 2 miles, the terrain around Key West has only modest variations in elevation — a maximum elevation change of 39 ft around an average of 3 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 75 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 52 ft.

The land around Key West is covered by water (64%) and artificial surfaces (26%) within 2 miles, water (95%) within 10 miles, and water (98%) within 50 miles.

2 miles
39 ft
10 miles
75 ft
50 miles
52 ft
treesgrasslandartificial surfacesbare terrainwatermangroves
September weather nearby: Marco Island 96 mi · Santa Cruz del Norte 98 mi · Alamar 101 mi · Cojímar 101 mi · Ciudad Camilo Cienfuegos 103 mi · Varadero 103 mi · Homestead 103 mi · Guanabacoa 104 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 Key West (24.5552°, -81.7816°, elevation 3 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).