Weather & Climate in Hercules, CA

Temperature, precipitation, air quality, natural hazards, and monthly weather data.

Hercules enjoys a temperate climate with an average annual temperature of 62°F (16°C). Winters average 50°F in January while summers reach 71°F in July. The area gets 326 sunny days per year, well above the U.S. average of 205 / making it one of the sunnier locations in the country. Annual precipitation totals 21.5 inches (drier than the 38-inch national average). Air quality is rated Good with a median AQI of 48. The city sits at an elevation of 13 feet.

Temperature

50°F Jan (10°C) 71°F Jul (21°C)

Annual Average	61.6°F
	14% above US avg
January Average	50°F (10°C)
July Average	71°F (21°C)
Sunny Days	326 days/yr

Geography

Elevation	13 ft (4 m)
Area	6.4 sq mi (16.6 km²)
Population Density	4,094/sq mi
Coordinates	38.0214°N, 122.2889°W
Timezone	America/Los_Angeles
County	Marin County County
Nearest Airport	Metro Oakland International (OAK) 21 miles away

Precipitation & Snow

Annual Rainfall 21.5"

43% below US avg

Wettest Month (Jan) 5.75"

Driest Month (Jul) 0.04"

Air Quality

AQI Median	48.0
Rating	Good

Natural Hazard Risk

Overall Risk	Relatively High
Risk Score	96.4 / 100
Social Vulnerability	24.7 / 100
Community Resilience	99.2 / 100

Hazard Breakdown

Tornado	Very Low
Earthquake	Relatively High
Wildfire	Relatively Moderate
Flood	Relatively High
Hail	Very Low
Strong Wind	Very Low
Heat Wave	Relatively Low
Winter Weather	Very Low
Lightning	Relatively Low
Drought	Relatively Low
Cold Wave	No Rating
Landslide	Relatively High
Coastal Flood	Very High
Tsunami	Relatively Moderate
Volcano	Very Low

Source: FEMA National Risk Index v1.20 (Dec 2025)

Earthquake History

4,815 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M6.0.

Aug 24, 2014	The 2014 South Napa, California Earthquake	M6.0	22 km	11 km
Apr 18, 1990	5 km NNW of Aromas, California	M5.4	133 km	5 km
Apr 18, 1990	4 km E of Interlaken, California	M5.1	130 km	7 km
Jan 16, 1993	9 km E of Gilroy, California	M4.9	133 km	7 km
May 14, 2002	5 km SSW of Gilroy, California	M4.9	132 km	7 km
Apr 18, 1990	4 km NNW of Aromas, California	M4.9	134 km	6 km
Sep 3, 2000	5 km WSW of Yountville, California	M4.9	41 km	9 km
Apr 19, 1996	2 km E of Aromas, California	M4.9	140 km	5 km
Sep 4, 1995	13 km SW of Middletown, California	M4.8	84 km	7 km
May 12, 2006	7 km W of Cobb, California	M4.7	100 km	4 km
May 21, 1996	8 km ESE of East Foothills, California	M4.7	89 km	8 km
Apr 18, 1990	4 km N of Aromas, California	M4.7	134 km	4 km
Aug 11, 1993	14 km ESE of Alum Rock, California	M4.7	95 km	9 km
Jan 2, 2025	4 km NW of Cobb, CA	M4.7	100 km	1 km
Mar 24, 1991	1 km NNE of Interlaken, California	M4.6	128 km	15 km
Aug 18, 1999	0 km S of Bolinas, California	M4.6	37 km	8 km
Jan 11, 2000	6 km N of Geyserville, California	M4.6	99 km	6 km
Feb 18, 2004	4 km WNW of Cobb, California	M4.6	100 km	3 km
Sep 19, 2023	15 km SW of Westley, CA	M4.5	109 km	4 km
Jan 12, 2014	8 km W of Cobb, California	M4.5	99 km	2 km

Source: USGS Earthquake Catalog (M2.5+, 1990-2025). Sorted by magnitude.

Tornado History

62 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF2. Total: 4 injuries.

Date	Rating	Distance	Path	Fatalities
May 5, 1998	EF2	76 km	0.6 mi	0
Jun 1, 1958	EF2	67 km	15.0 mi	0
Jan 11, 1951	EF2	74 km	5.7 mi	0
Mar 18, 2011	EF1	60 km	0.1 mi	0
Jan 23, 2010	EF1	47 km	1.6 mi	0
Mar 20, 2005	EF1	43 km	3.0 mi	0
Jan 27, 2005	EF1	98 km	0.5 mi	0
Dec 5, 1998	EF1	60 km	1.5 mi	0
May 5, 1998	EF1	73 km	0.3 mi	0
Dec 23, 1996	EF1	62 km	6.0 mi	0
Feb 22, 1996	EF1	70 km	1.0 mi	0
Dec 2, 1992	EF1	68 km	7.5 mi	0
Dec 2, 1992	EF1	75 km	3.0 mi	0
Dec 2, 1992	EF1	63 km	1.0 mi	0
Feb 27, 1983	EF1	60 km	0.8 mi	0
Jan 14, 1980	EF1	70 km	0.3 mi	0
May 31, 1967	EF1	87 km	0.1 mi	0
Nov 10, 1964	EF1	72 km	1.0 mi	0
Apr 1, 1958	EF1	45 km	0.2 mi	0
Nov 8, 2022	EF0	91 km	0.8 mi	0

Source: NOAA Storm Prediction Center (EF0+, 1950-2024, US only).

Tsunami History

5 tsunamis recorded within 500 km. Highest wave on record: 4.5 m (15 ft).

Year	Location	Cause	Max Wave	Deaths	Distance
1868	N. CALIFORNIA	Eruption + Earthquake	4.5 m	30	39 km
1989	N. CALIFORNIA	Earthquake	1.0 m	62	115 km
1856	N. CALIFORNIA	Eruption + Earthquake	0.6 m	-	58 km
1906	N. CALIFORNIA	Eruption + Earthquake	0.1 m	-	40 km
1865	N. CALIFORNIA	Eruption + Earthquake	-	-	98 km

Source: NOAA/NCEI Historical Tsunami Database.

Nearby Volcanoes

1 volcano within 200 km. Closest: Clear Lake (114 km).

Name	Type	Elevation	Last Eruption	Distance
Clear Lake	Volcanic field	1,439 m (4,721 ft)	Unknown	114 km

Source: Smithsonian Institution Global Volcanism Program (GVP).

Wildfire History

20 wildfires (100+ acres) recorded within 100 km. Largest: SCU LIGHTNING COMPLEX (405,787 acres, 2020).

Year	Name	Acres Burned	Distance
2020	SCU LIGHTNING COMPLEX	405,787	91 km
2020	HENNESSEY	314,241	67 km
2015	ROCKY	96,125	100 km
2018	COUNTY	92,450	75 km
2020	CZU AUG LIGHTNING	85,894	98 km
2019	KINCADE	77,780	84 km
2015	VALLEY	77,507	90 km
2020	GLASS	68,020	63 km
2017	NUNS	56,883	41 km
2020	WALLBRIDGE	55,194	91 km
2017	ATLAS	51,664	38 km
2004	RUMSEY	39,335	82 km
1999	SIXTEEN	37,162	87 km
2017	TUBBS	36,981	70 km
1988	MILLER	35,750	49 km
2017	POCKET	18,691	98 km
2024	CORRAL	16,138	85 km
2006	ZAM ASSIST	14,404	88 km
2004	GEYSERS	12,075	88 km
2009	CORRAL	12,006	85 km

Source: NIFC/IRWIN Wildfire Records (100+ acres).

Monthly Weather

Month	Avg Temperature	Precipitation	Summary
January	50°F (10°C)	5.8 in	Wettest
February	52°F (11°C)	4.9 in
March	54°F (12°C)	3.9 in
April	58°F (14°C)	1.4 in
May	63°F (17°C)	0.6 in
June	68°F (20°C)	0.2 in
July	71°F (21°C)	0.0 in	Warmest, Driest
August	71°F (21°C)	0.1 in
September	69°F (20°C)	0.3 in
October	63°F (17°C)	1.5 in
November	54°F (12°C)	3.9 in
December	47°F (8°C)	4.2 in	Coldest

Hercules has a seasonal temperature swing of 23°F / from 47°F in December to 71°F in July. Total annual precipitation is 26.7 inches, with January being the wettest month (5.8") and July the driest (0.0").

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