San Carlos weather in September

In September, San Carlos sees average daytime highs of 74°F and overnight lows near 57°F, with 0.1 in of rain across 0.4 wet days and about 12.3 hours of daylight. It is the 1st-warmest and 10th-wettest month of the year here.

Day-to-day highs hold fairly steady near 74°F through the month. The sky is clear or mostly clear about 79% of the time in September, and the air most often feels dry.

Daylight stretches from about 12 h 48 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is San Carlos's 1st-clearest and 10th-windiest month. For the whole year in context, see San Carlos's year-round climate.

Daytime high
74°
1st warmest
Overnight low
57°
11th coldest
Rainfall
0.1 in
0.4 wet days
Daylight
12 h 12 min
5:56 AM – 6:10 PM
Cloud cover
22%
1st clearest
Wind
4 mph
10th windiest
Solar energy
5.75 kWh/m²
Travel score
9.2
out of 10

San Carlos is city in San Mateo County, California, United States.

Density
2,096/km²
people per km²
Founded
1925

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 74°F through the month.

A typical September day in San Carlos reaches about 74°F in the afternoon and slips back to 57°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 67°F and 84°F. Set against its neighbours, September runs on par with August and about 3°F warmer than October.

50°60°70°80°151015202530
Avg high (°F)Avg low (°F)
17457
27457
37457
47457
57457
67457
77457
87457
97457
107457
117457
127457
137457
147457
157457
167457
177457
187457
197457
207457
217457
227456
237456
247456
257456
267456
277456
287456
297456
307456

San Carlos weather by month

How September compares with the rest of the year at a glance. September is the 1st-warmest and 10th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysDaylight (hours)Travel score
Jan57° / 45°3.99.49.74.1
Feb59° / 47°4.29.310.64.5
Mar61° / 48°3.29.111.75.3
Apr63° / 49°1.65.612.96.4
May66° / 52°0.83.3147.4
Jun70° / 54°0.20.914.58.5
Jul73° / 56°0.00.214.39.1
Aug74° / 57°0.00.113.49.2
Sep74° / 57°0.10.412.39.2
Oct71° / 54°0.93118.2
Nov63° / 49°2.06106.1
Dec57° / 46°3.79.39.54.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 79% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 10% of September, with mostly cloudy or overcast conditions the remaining 11%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
1937
2937
3937
4937
5928
6919
7919
8919
9919
10919
11919
12919
138911
148911
158911
169010
179010
188911
198911
208911
218812
228812
238812
248713
258614
268515
278515
288515
298416
308416

Chance of precipitation in September

Any precipitation

San Carlos gets around 0.1 in of rain over 0.4 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 2% and peaks near 4% on the wettest days.

0%10%20%30%151015202530
Rain chance (%)
10
20
30
40
51
61
71
81
91
101
111
121
131
141
152
162
172
182
192
202
212
222
232
243
253
263
273
284
294
304

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 55% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)
146494
247494
348484
449474
549474
650464
751454
852453
953443
1053443
1154433
1254433
1354433
1454433
1554433
1654433
1754433
1855423
1955423
2056413
2157412
2258402
2359392
2459392
2560382
2661372
2763352
2864342
2966322
3067312

Wind in September

Winds average 4 mph in September.

Across September, daily wind ranges from about 4 mph on the calmest days to 5 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
15calm
25calm
35calm
45calm
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 48 min at the start of September to 11 h 42 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 66 minutes over September. Sunrise moves from 5:43 AM to 6:09 AM, and sunset from 6:34 PM to 5:48 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.85:436:34
212.85:446:33
312.85:456:31
412.75:466:30
512.75:476:28
612.65:486:26
712.65:496:25
812.65:496:23
912.55:506:22
1012.55:516:20
1112.45:526:18
1212.45:536:17
1312.45:546:15
1412.35:556:14
1512.35:556:12
1612.25:566:10
1712.25:576:09
1812.25:586:07
1912.15:596:06
2012.16:006:04
2112.06:016:02
2212.06:016:01
2311.96:025:59
2411.96:035:58
2511.96:045:56
2611.86:055:54
2711.86:065:53
2811.76:075:51
2911.76:085:50
3011.76:095:48

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.75 kWh/m².

For context, solar energy here swings from a low near 2.27 kWh/m² to a high of 7.76 kWh/m² in June across the year — September's 5.75 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
16.3Intense
26.3Intense
36.3Intense
46.2Intense
56.2Intense
66.2Intense
76.1Intense
86.1Intense
96.0Intense
106.0Bright
115.9Bright
125.9Bright
135.8Bright
145.8Bright
155.8Bright
165.7Bright
175.7Bright
185.6Bright
195.6Bright
205.5Bright
215.5Bright
225.5Bright
235.4Bright
245.4Bright
255.3Bright
265.3Bright
275.2Bright
285.2Bright
295.1Bright
305.1Bright
Planning a trip in September

Hazard calendar for San Carlos

In seasonPeak

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

San Carlos'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 San Carlos?

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

9.2
Sightseeing
1st-best month of the year
7.3
Beach & pool
1st-best month of the year

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

What to pack for San Carlos in September

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

In September, San Carlos sees daytime highs around 74°F and nights near 57°F. Worth packing: light clothes and sun protection.

light clothessun protection

Sea temperature near San Carlos in September

The nearest coast averages about 59°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 11 mi away) is warmest in August at about 59°F and coldest in April near 54°F.

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

52°54°56°58°60°JanFebMarAprMayJunJulAugSepOctNovDecbracingcool
Sea temperature (°F)Comfort
Jan54Bracing
Feb54Bracing
Mar54Bracing
Apr54Bracing
May54Bracing
Jun55Bracing
Jul57Bracing
Aug59Bracing
Sep59Bracing
Oct58Bracing
Nov56Bracing
Dec55Bracing

UV index in San Carlos 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 San Carlos peaks around June 23 at about 10 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 15 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 15UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar5Moderate
Apr6High
May8Very high
Jun10Extreme
Jul10Extreme
Aug10Very high
Sep6High
Oct5High
Nov2Moderate
Dec2Moderate

Air quality in San Carlos 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 San Carlos is worst in August — around 25 µg/m³ PM2.5 (moderate), about 2.5× the cleanest month (June, 10 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateAug 1824 µg/m³Jun 1110 µg/m³
PM2.5 (µg/m³)Level
Jan15Moderate
Feb18Moderate
Mar16Moderate
Apr12Moderate
May10Good
Jun10Good
Jul11Good
Aug25Moderate
Sep17Moderate
Oct20Moderate
Nov18Moderate
Dec13Moderate
Location & terrain

Where is San Carlos?

San Carlos sits at 37.5°N, 122.3°W, 33 ft above sea level, in United States. The nearest listed city is Belmont, 1.2 mi away.

Topography around San Carlos

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

Within 2 miles, the terrain around San Carlos has significant variations in elevation — a maximum elevation change of 902 ft around an average of 121 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 2,454 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 4,452 ft.

The land around San Carlos is covered by artificial surfaces (50%) and trees (27%) within 2 miles, trees (39%) and water (33%) within 10 miles, and water (40%), trees (24%) and grassland (21%) within 50 miles.

2 miles
902 ft
10 miles
2,454 ft
50 miles
4,452 ft
treesshrubsgrasslandcroplandartificial surfacesbare terrainwaterwetland
September weather nearby: Belmont 1.2 mi · Redwood City 1.9 mi · Foster City 3.7 mi · San Mateo 5.0 mi · Menlo Park 5.6 mi · East Palo Alto 6.8 mi · Burlingame 8.1 mi · Palo Alto 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 San Carlos (37.5072°, -122.2605°, elevation 33 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).