September weather forecast and climate
Diablo, CA

Weather in September

September, the first month of the autumn, in Diablo, is also a moderately hot month, with temperature in the range of an average low of 56.7°F (13.7°C) and an average high of 82°F (27.8°C).

Temperature

In Diablo, the average high-temperature is essentially the same as in August - a still moderately hot 82°F (27.8°C). In September, in Diablo, the average low-temperature is 56.7°F (13.7°C).

Heat index

In September, the average heat index is estimated at 84°F (28.9°C). Exhaustion is likely with prolonged exposure and activity. Sustaining activity may result in heat cramps.
Note that heat index values are valued for light wind and location in the shade. Exposure to direct sunshine can increase heat index values by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'felt air temperature', 'real feel', 'apparent temperature', or 'feels like', is a measure of how hot it feels when the actual air humidity is factored in. Additional factors like wind, metabolic differences, differences in body mass, height, and shape, and activity influence one's weather impression. Be aware that direct exposure to sunlight increases heat impact, and may raise the heat index additionally, by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are particularly important for children. Children are often less aware of the need to rest and re-hydrate. Thirst is a late sign of dehydration - it is vital to remain hydrated, particularly during prolonged physical activities.

Humidity

September is the least humid month in Diablo, with an average relative humidity of 57%.

Rainfall

Months with rainfall in Diablo are January through June, September through December. September is the first month it rains in Diablo. Throughout September, in the average 1.7 rainfall days, it receives 0.08" (2mm) of precipitation. Throughout the year, there are 65.6 rainfall days, and 11.22" (285mm) of precipitation is accumulated.

Daylight

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

Sunshine

In September, the average sunshine in Diablo is 11.1h.

UV index

In September, the average daily maximum UV index is 5. A UV Index of 3 to 5 symbolizes a moderate health risk from the exposure to the Sun's UV rays for the average person.
Note: In September, the average maximum UV index of 5 translate into the following recommendations:
Take precautions - Protection against sun damage is advised. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. A wide-brim hat offers excellent sun protection for eyes, ears, face, and neck. Sunglasses with UVA and UVB protection significantly reduce eye damage from sun exposure. Tightly woven, loose-fitting clothes provide additional protection from the Sun.
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FAQ

What is the temperature in September in Diablo?

In Diablo, in September, the average high-temperature is 82°F (27.8°C), and the average low-temperature is 56.7°F (13.7°C). In September, the average heat index (a.k.a. 'felt air temperature', 'feels like'), that combines both air temperature and relative humidity, is estimated at 84°F (28.9°C).

What is the least humid month in Diablo?

September is the least humid month, with an average relative humidity of 57%.

What is the average humidity in September in Diablo?

The average relative humidity in September in Diablo, California, is 57%.

When does it start to rain in Diablo?

September is the first month it rains in Diablo. Throughout September, in the average 1.7 rainfall days, it receives 0.08" (2mm) of precipitation.

How many hours of daylight does Diablo have in September?

The average length of the day in September in Diablo is 12.4h.

How many hours of sunshine does Diablo have in September?

In September, the average sunshine in Diablo is 11.1h.

What is the UV index reading in September in Diablo?

In September, the average daily maximum UV index in Diablo, California, is 5. A UV Index estimate of 3 to 5 represents a medium health risk from unprotected exposure to the UV radiation.

Average temperature in September
Diablo, CA

Average temperature in September - Diablo, CA
  • Average high temperature in September: 82°F

The warmest month (with the highest average high temperature) is July (83.8°F).
The month with the lowest average high temperature is December (55.8°F).

  • Average low temperature in September: 56.7°F

Months with the highest average low temperature are August and September (56.7°F).
The coldest month (with the lowest average low temperature) is January (42.1°F).

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Average pressure in September
Diablo, CA

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

The month with the highest atmospheric pressure is January (30.14").
Months with the lowest atmospheric pressure are June, August and September (29.92").

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Average wind speed in September
Diablo, CA

Average wind speed in September - Diablo, CA
  • Average wind speed in September: 5.4mph

The windiest month (with the highest average wind speed) is May (6.9mph).
The calmest month (with the lowest average wind speed) is November (4.3mph).

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Average humidity in September
Diablo, CA

Average humidity in September - Diablo, CA
  • Average humidity in September: 57%

The month with the highest relative humidity is March (74%).
The month with the lowest relative humidity is September (57%).

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Average rainfall in September
Diablo, CA

Average rainfall in September - Diablo, CA
  • Average rainfall in September: 0.08"

The wettest month (with the highest rainfall) is February (2.36").
The driest months (with the least rainfall) are July and August (0").

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Average rainfall days in September
Diablo, CA

Average rainfall days in September - Diablo, CA
  • Average rainfall days in September: 1.7 days

The month with the highest number of rainy days is March (12.6 days).
The month with the least rainy days is August (0.6 days).

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

Average daylight in September / Average sunshine in September - Diablo, 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: 11.1h

The month with the most sunshine is July (Average sunshine: 12.1h).
The month with the least sunshine is December (Average sunshine: 5.8h).

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Average sunshine days in September
Diablo, CA

Average sunshine days in September - Diablo, CA
  • Average sunshine days in September: 27.2 days

The month with the most sunshine days is July (30.2 days).
The month with the least sunshine days is March (17.6 days).

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Average UV index in September
Diablo, CA

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

Months with the highest UV index are June, July and August (UV index 6).
Months with the lowest UV index are January, February, November and December (UV index 3).

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Average cloud cover in September
Diablo, CA

Average cloud cover in September - Diablo, CA
  • Average cloud cover in September: 10

The month with the most cloud cover is March (Cloud cover 36).
The month with the least cloud cover is July (Cloud cover 6).

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Average visibility in September
Diablo, CA

Average visibility in September - Diablo, 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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