Hercules weather in September

In September, Hercules sees average daytime highs of 81°F and overnight lows near 55°F, with 0.1 in of rain across 0.4 wet days and about 12.3 hours of daylight. It is the 2nd-warmest and 10th-wettest month of the year here.

Day-to-day highs hold fairly steady near 81°F through the month. The sky is clear or mostly clear about 86% 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 42 min by month's end. Set against the rest of the year, September is Hercules's 3rd-clearest and 6th-windiest month. For the whole year in context, see Hercules's year-round climate.

Daytime high
81°
2nd warmest
Overnight low
55°
10th coldest
Rainfall
0.1 in
0.4 wet days
Daylight
12 h 12 min
5:56 AM – 6:11 PM
Cloud cover
15%
3rd clearest
Wind
6 mph
6th windiest
Solar energy
5.88 kWh/m²
Travel score
8.8
out of 10

Hercules is city in western Contra Costa County, California, United States.

Density
489/km²
people per km²
Founded
1900

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 81°F through the month.

A typical September day in Hercules reaches about 81°F in the afternoon and slips back to 55°F overnight — a 25°F spread between the day's warmth and the night's chill. On most days the high lands between 72°F and 92°F. Set against its neighbours, September runs on par with August and about 5°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18256
28256
38256
48256
58256
68256
78156
88156
98156
108156
118156
128155
138155
148155
158155
168055
178055
188055
198055
208055
218055
228055
238055
248055
258055
268054
278054
288054
297954
307954

Hercules weather by month

How September compares with the rest of the year at a glance. September is the 2nd-warmest and 10th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysDaylight (hours)Travel score
Jan57° / 42°4.09.39.74.2
Feb61° / 44°4.28.810.55.0
Mar64° / 46°3.18.711.76.1
Apr68° / 48°1.44.9137.3
May74° / 52°0.73148.4
Jun79° / 55°0.20.814.68.9
Jul80° / 56°0.00.114.49.0
Aug81° / 56°0.00.213.58.9
Sep81° / 55°0.10.412.38.8
Oct75° / 52°0.93118.5
Nov65° / 46°1.95.69.96.5
Dec57° / 42°3.79.39.44.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 86% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 6% 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 (%)
1964
2964
3964
4964
5964
6964
7964
8964
9955
10955
11955
12955
13955
14937
15937
16937
17928
18928
19919
20919
219010
229010
238911
248911
258812
268812
278713
288713
298614
308614

Chance of precipitation in September

Any precipitation

Hercules 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 (%)
11
21
31
41
51
61
71
81
91
101
111
121
131
141
151
162
172
182
192
202
212
222
232
242
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 81% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)
177221
277221
378211
478211
579201
679201
779201
879192
979192
1079192
1180182
1280182
1381181
1481181
1581181
1681181
1782171
1882171
1982171
2082171
2183161
2283161
2383161
2484151
2584151
2685141
2785141
2886131
2986131
3087121

Wind in September

Winds average 6 mph in September.

Across September, daily wind ranges from about 5 mph on the calmest days to 6 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
16calm
26calm
36calm
46calm
56calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
235calm
245calm
255calm
265calm
275calm
285calm
295calm
305calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 54 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 72 minutes over September. Sunrise moves from 5:43 AM to 6:09 AM, and sunset from 6:35 PM to 5:48 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:436:35
212.85:446:33
312.85:456:32
412.75:466:30
512.75:476:28
612.75:476:27
712.65:486:25
812.65:496:24
912.55:506:22
1012.55:516:20
1112.55:526:19
1212.45:536:17
1312.45:546:16
1412.35:546:14
1512.35:556:12
1612.25:566:11
1712.25:576:09
1812.25:586:07
1912.15:596:06
2012.16:006:04
2112.06:016:03
2212.06:026:01
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 5.88 kWh/m².

For context, solar energy here swings from a low near 2.13 kWh/m² to a high of 7.96 kWh/m² in June across the year — September's 5.88 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
16.6Intense
26.5Intense
36.5Intense
46.4Intense
56.4Intense
66.3Intense
76.3Intense
86.3Intense
96.2Intense
106.2Intense
116.1Intense
126.0Intense
136.0Intense
146.0Bright
155.9Bright
165.8Bright
175.8Bright
185.7Bright
195.7Bright
205.6Bright
215.6Bright
225.5Bright
235.5Bright
245.4Bright
255.4Bright
265.3Bright
275.3Bright
285.2Bright
295.2Bright
305.1Bright
Planning a trip in September

Hazard calendar for Hercules

In seasonPeak

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

Hercules'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 Hercules?

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

8.8
Sightseeing
4th-best month of the year
8.8
Beach & pool
3rd-best month of the year

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

What to pack for Hercules in September

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

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

light clothessun protection

Sea temperature near Hercules in September

The nearest coast averages about 58°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 58°F and coldest in April near 53°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
Jan53Bracing
Feb53Bracing
Mar54Bracing
Apr53Bracing
May53Bracing
Jun54Bracing
Jul56Bracing
Aug58Bracing
Sep58Bracing
Oct57Bracing
Nov55Bracing
Dec54Bracing

UV index in Hercules 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 Hercules peaks around July 11 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 highHighModerateJul 11UV 10Dec 15UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar5Moderate
Apr6High
May8Very high
Jun10Extreme
Jul10Extreme
Aug10Very high
Sep6High
Oct5High
Nov2Moderate
Dec2Low

Air quality in Hercules 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 Hercules is worst in September — around 29 µg/m³ PM2.5 (moderate), about 4.2× the cleanest month (June, 7 µg/m³).

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

010203040JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateSep 1829 µg/m³Jun 127 µg/m³
PM2.5 (µg/m³)Level
Jan13Moderate
Feb13Moderate
Mar13Moderate
Apr10Good
May8Good
Jun7Good
Jul10Good
Aug25Moderate
Sep29Moderate
Oct27Moderate
Nov16Moderate
Dec12Good
Location & terrain

Where is Hercules?

Hercules sits at 38.0°N, 122.3°W, 79 ft above sea level, in United States. The nearest listed city is Pinole, 1.2 mi away.

Topography around Hercules

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

Within 2 miles, the terrain around Hercules has only modest variations in elevation — a maximum elevation change of 564 ft around an average of 75 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 2,126 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 4,459 ft.

The land around Hercules is covered by water (41%) and artificial surfaces (36%) within 2 miles, water (41%), grassland (20%) and artificial surfaces (20%) within 10 miles, and water (28%), grassland (27%) and trees (23%) within 50 miles.

2 miles
564 ft
10 miles
2,126 ft
50 miles
4,459 ft
treesshrubsgrasslandcroplandartificial surfacesbare terrainwaterwetland
September weather nearby: Pinole 1.2 mi · San Pablo 5.0 mi · Vallejo 6.2 mi · Richmond 6.2 mi · El Cerrito 6.8 mi · Benicia 7.5 mi · Martinez 8.7 mi · Albany 8.7 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 Hercules (38.0171°, -122.2886°, elevation 79 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).