Windsor weather in September

In September, Windsor sees average daytime highs of 81°F and overnight lows near 55°F, with 0.1 in of rain across 0.6 wet days and about 12.3 hours of daylight. It is the 3rd-warmest and 10th-wettest month of the year here.

Highs ease over the month, from about 83°F in the first days to 79°F by the end. The sky is clear or mostly clear about 85% 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 Windsor's 3rd-clearest and 11th-windiest month. For the whole year in context, see Windsor's year-round climate.

Daytime high
81°
3rd warmest
Overnight low
55°
9th coldest
Rainfall
0.1 in
0.6 wet days
Daylight
12 h 12 min
5:58 AM – 6:13 PM
Cloud cover
15%
3rd clearest
Wind
4 mph
11th windiest
Solar energy
5.89 kWh/m²
Travel score
8.6
out of 10

Windsor is town in Sonoma County, California, United States.

Density
1,454/km²
people per km²
Founded
1992

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 83°F in the first days to 79°F by the end.

A typical September day in Windsor reaches about 81°F in the afternoon and slips back to 55°F overnight — a 26°F spread between the day's warmth and the night's chill. On most days the high lands between 72°F and 91°F. Set against its neighbours, September runs about 2°F cooler than August and about 7°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18357
28357
38356
48356
58356
68356
78256
88256
98256
108256
118256
128255
138255
148155
158155
168155
178155
188155
198155
208155
218155
228155
238054
248054
258054
268054
278054
288054
297953
307953

Windsor weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 10th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysDaylight (hours)Travel score
Jan57° / 40°5.710.39.64.0
Feb60° / 42°5.89.310.54.7
Mar63° / 44°4.49.511.75.7
Apr67° / 46°1.95.6137.0
May73° / 51°1.13.614.18.2
Jun80° / 55°0.31.214.68.5
Jul83° / 57°0.00.114.47.8
Aug83° / 57°0.00.213.57.8
Sep81° / 55°0.10.612.38.6
Oct74° / 50°1.43.2118.5
Nov63° / 44°3.06.29.96.2
Dec56° / 39°5.910.19.43.9

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 85% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 7% of September, with mostly cloudy or overcast conditions the remaining 8%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
1955
2955
3955
4955
5946
6946
7946
8946
9946
10937
11937
12937
13937
14937
15937
16937
17928
18928
19928
20928
21928
22919
23919
24919
259010
269010
278911
288911
298911
308812

Chance of precipitation in September

Any precipitation

Windsor gets around 0.1 in of rain over 0.6 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 3% and peaks near 5% on the wettest days.

0%10%20%30%151015202530
Rain chance (%)
11
21
31
41
51
61
71
81
91
101
112
122
132
142
152
162
173
183
193
203
213
223
234
244
254
264
275
285
295
305

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 88% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)
181181
282171
383161
484151
584151
685141
785141
886131
986131
1086131
1187121
1287121
1387121
1487121
1587121
1688120
1788120
1888120
1989110
2089110
2189101
2289101
239091
249091
259181
269181
279271
289271
299361
309361

Wind in September

Winds average 4 mph in September.

Across September, daily wind ranges from about 4 mph on the calmest days to 4 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
14calm
24calm
34calm
44calm
54calm
64calm
74calm
84calm
94calm
104calm
114calm
124calm
134calm
144calm
154calm
164calm
174calm
184calm
194calm
204calm
214calm
224calm
234calm
244calm
254calm
264calm
274calm
284calm
294calm
304calm

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 5:45 AM to 6:11 AM, and sunset from 6:37 PM to 5:50 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:456:37
212.85:466:36
312.85:466:34
412.85:476:33
512.75:486:31
612.75:496:29
712.65:506:28
812.65:516:26
912.55:526:25
1012.55:536:23
1112.55:546:21
1212.45:556:20
1312.45:556:18
1412.35:566:16
1512.35:576:15
1612.25:586:13
1712.25:596:11
1812.26:006:10
1912.16:016:08
2012.16:026:06
2112.06:036:05
2212.06:046:03
2311.96:056:01
2411.96:066:00
2511.96:065:58
2611.86:075:56
2711.86:085:55
2811.76:095:53
2911.76:105:52
3011.66:115:50

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.89 kWh/m².

For context, solar energy here swings from a low near 2.08 kWh/m² to a high of 8.01 kWh/m² in June across the year — September's 5.89 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
16.6Intense
26.5Intense
36.5Intense
46.5Intense
56.4Intense
66.4Intense
76.3Intense
86.3Intense
96.2Intense
106.2Intense
116.1Intense
126.1Intense
136.0Intense
146.0Bright
155.9Bright
165.8Bright
175.8Bright
185.8Bright
195.7Bright
205.6Bright
215.6Bright
225.5Bright
235.5Bright
245.4Bright
255.4Bright
265.3Bright
275.3Bright
285.2Bright
295.1Bright
305.1Bright
Planning a trip in September

Hazard calendar for Windsor

In seasonPeak

None of Windsor's seasonal hazards are active in September. The full-year calendar below shows when the rainy season, cyclone risk and dust haze do peak.

Windsor's rainy season runs November–March, when most of the year's rain falls.

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

Is September a good time to visit Windsor?

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

8.6
Sightseeing
1st-best month of the year
8.9
Beach & pool
3rd-best month of the year

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

What to pack for Windsor in September

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

In September, Windsor sees daytime highs around 81°F and nights near 55°F. Pack light clothes. Worth having: sun protection.

light clothessun protection

Sea temperature near Windsor in September

The nearest coast averages about 55°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 21 mi away) is warmest in September at about 55°F and coldest in May near 51°F.

The water stays below 68°F all year — cool enough that most swimmers want a wetsuit.

50°52°54°56°JanFebMarAprMayJunJulAugSepOctNovDecbracing
Sea temperature (°F)Comfort
Jan53Bracing
Feb53Bracing
Mar53Bracing
Apr51Bracing
May51Bracing
Jun51Bracing
Jul53Bracing
Aug54Bracing
Sep55Bracing
Oct55Bracing
Nov54Bracing
Dec53Bracing

UV index in Windsor 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 Windsor peaks around June 23 at about 10 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 17 at about 2 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 9 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highExtremeVery highHighModerateJun 23UV 10Dec 17UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar5Moderate
Apr6High
May9Very high
Jun10Extreme
Jul10Extreme
Aug9Very high
Sep6High
Oct5High
Nov2Moderate
Dec2Low

Air quality in Windsor 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 Windsor is worst in September — around 24 µg/m³ PM2.5 (moderate), about 4.1× the cleanest month (June, 6 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodSep 1623 µg/m³Jun 116 µg/m³
PM2.5 (µg/m³)Level
Jan8Good
Feb9Good
Mar9Good
Apr7Good
May7Good
Jun6Good
Jul9Good
Aug17Moderate
Sep24Moderate
Oct16Moderate
Nov9Good
Dec7Good
Location & terrain

Where is Windsor?

Windsor sits at 38.5°N, 122.8°W, 118 ft above sea level, in United States. The nearest listed city is Santa Rosa, 9.3 mi away.

Topography around Windsor

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

Within 2 miles, the terrain around Windsor has only modest variations in elevation — a maximum elevation change of 476 ft around an average of 144 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 1,969 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 6,266 ft.

The land around Windsor is covered by trees (35%), artificial surfaces (28%) and grassland (26%) within 2 miles, trees (57%) and grassland (27%) within 10 miles, and trees (42%), grassland (27%) and water (24%) within 50 miles.

2 miles
476 ft
10 miles
1,969 ft
50 miles
6,266 ft
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Santa Rosa 9.3 mi · Rohnert Park 16 mi · Agua Caliente 24 mi · Petaluma 24 mi · Clearlake 30 mi · Novato 33 mi · Napa 34 mi · American Canyon 40 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 Windsor (38.5471°, -122.8164°, elevation 118 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. 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).