September weather forecast and climate
Hercules, CA

Weather in September

September, the first month of the autumn, in Hercules, is still a warm month, with average temperature ranging between min 56.7°F (13.7°C) and max 77.5°F (25.3°C).

Temperature

With an average high-temperature of 77.5°F (25.3°C) and an average low-temperature of 56.7°F (13.7°C), September is the warmest month.

Humidity

September and October, with an average relative humidity of 63%, are the least humid months.

Rainfall

In September, in Hercules, California, the rain falls for 2.3 days. Throughout September, 0.12" (3mm) of precipitation is accumulated. Throughout the year, there are 72.2 rainfall days, and 12.83" (326mm) of precipitation is accumulated.

Ocean temperature

September is the month with the warmest seawater in Hercules, California, with an average ocean temperature of 57°F (13.9°C).
Note: Swimming in 57°F (13.9°C) is considered life-threatening. Even a few minutes in 55.4°F (13°C) water is uncomfortable, and swimming below 50°F (10°C) may cause total loss of breathing control and cold shock, depending on a person's physique.

Daylight

The average length of the day is 12.4h.

Sunshine

In Hercules, the average sunshine is 10.9h.

UV index

Months with the highest UV index in Hercules are April through September, with an average maximum UV index of 5. A UV Index of 3 to 5 symbolizes a medium vulnerability from unsafe exposure to the UV radiation for the average person.
Note: In September, the average maximum UV index of 5 translate into the following recommendations:
Take precautions - Protection against sunburn is recommended. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes.
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FAQ

What is the warmest month in Hercules?

The warmest month in Hercules is September, with an average high-temperature of 77.5°F (25.3°C) and an average low-temperature of 56.7°F (13.7°C).

What is the temperature in September in Hercules?

In Hercules, in September, the average high-temperature is 77.5°F (25.3°C), and the average low-temperature is 56.7°F (13.7°C).

What is the least humid month in Hercules?

September and October, with an average relative humidity of 63%, are the least humid months in Hercules.

What is the average humidity in September in Hercules?

In Hercules, California, the average relative humidity in September is 63%.

How many days does it rain in September in Hercules?

In Hercules, California, in September, during 2.3 rainfall days, 0.12" (3mm) of precipitation is typically accumulated.

What month is the ocean warmest in Hercules?

The month with the warmest seawater in Hercules, California, is September, with an average ocean temperature of 57°F (13.9°C).

How cold is the water in September in Hercules?

In September, the average ocean temperature in Hercules, California, is 57°F (13.9°C). At temperatures below 50°F (10°C), swimming in a suitably protected swimsuit is feasible; otherwise, cold shock and loss of breathing control are imminent. Even a short swim, without thermal protection, at temperatures around 55.4°F (13°C) is not comfortable.

What is the average length of the day in September in Hercules?

In Hercules, the average length of the day in September is 12.4h.

How long on average sun shines in September in Hercules?

The average sunshine in September in Hercules, California, is 10.9h.

When is the highest UV index in Hercules?

April through September, with an average maximum UV index of 5, are months with the highest UV index in Hercules.

What is the UV index intensity in September in Hercules?

In September, the average daily maximum UV index in Hercules, California, is 5. A UV Index reading of 3 to 5 represents a moderate vulnerability from unprotected exposure to the UV radiation.

Average temperature in September
Hercules, CA

Average temperature in September - Hercules, CA
  • Average high temperature in September: 77.5°F

The warmest month (with the highest average high temperature) is September (77.5°F).
The month with the lowest average high temperature is December (55.4°F).

  • Average low temperature in September: 56.7°F

The month with the highest average low temperature is August (56.8°F).
The coldest months (with the lowest average low temperature) are January and December (43.9°F).

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Average pressure in September
Hercules, CA

Average pressure in September - Hercules, CA
  • Average pressure in September: 29.92"

The month with the highest atmospheric pressure is January (30.13").
Months with the lowest atmospheric pressure are June, August and September (29.92").

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Average wind speed in September
Hercules, CA

Average wind speed in September - Hercules, CA
  • Average wind speed in September: 5.7mph

The windiest month (with the highest average wind speed) is May (7.5mph).
The calmest month (with the lowest average wind speed) is November (4.8mph).

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Average humidity in September
Hercules, CA

Average humidity in September - Hercules, CA
  • Average humidity in September: 63%

The month with the highest relative humidity is March (74%).
Months with the lowest relative humidity are September and October (63%).

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Average rainfall in September
Hercules, CA

Average rainfall in September - Hercules, CA
  • Average rainfall in September: 0.12"

The wettest month (with the highest rainfall) is February (2.76").
The driest months (with the least rainfall) are July and August (0.04").

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Average rainfall days in September
Hercules, CA

Average rainfall days in September - Hercules, CA
  • Average rainfall days in September: 2.3 days

The month with the highest number of rainy days is March (12.6 days).
The month with the least rainy days is August (1.1 days).

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Average sea temperature in September
Hercules, CA

Average sea temperature in September - Hercules, CA
  • Average sea temperature in September: 57°F

The best month for swimming (with the highest average sea temperature) is September (57°F).
The coldest month (with the lowest average sea temperature) is April (52.6°F).

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Average daylight in September /
Average sunshine in September
Hercules, CA

Average daylight in September / Average sunshine in September - Hercules, CA
  • Average daylight in September: 12.4h

The month with the longest days is June (Average daylight: 14.8h).
The month with the shortest days is December (Average daylight: 9.6h).

  • Average sunshine in September: 10.9h

The month with the most sunshine is July (Average sunshine: 11.9h).
The month with the least sunshine is December (Average sunshine: 5.7h).

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Average sunshine days in September
Hercules, CA

Average sunshine days in September - Hercules, CA
  • Average sunshine days in September: 25.9 days

The month with the most sunshine days is August (27.3 days).
The month with the least sunshine days is March (16.4 days).

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Average UV index in September
Hercules, CA

Average UV index in September - Hercules, CA
  • Average UV index in September: 5

Months with the highest UV index are April, May, June, July, August and September (UV index 5).
Months with the lowest UV index are January, February, November and December (UV index 3).

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Average cloud cover in September
Hercules, CA

Average cloud cover in September - Hercules, CA
  • Average cloud cover in September: 13

The month with the most cloud cover is March (Cloud cover 37).
The month with the least cloud cover is July (Cloud cover 12).

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Average visibility in September
Hercules, CA

Average visibility in September - Hercules, CA
  • Average visibility in September: 6mi

Months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
Months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

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