September weather forecast
Sonoma, CA

Neat rows of vines in a vineyard farm in Sonoma, California
Neat rows of vines in a vineyard farm in Sonoma, California

Weather in September

The first month of the autumn, September, is still a warm month in Sonoma, California, with an average temperature varying between 81.1°F (27.3°C) and 54.7°F (12.6°C).

Temperature

In September, the average high-temperature is practically the same as in August - a still moderately hot 81.1°F (27.3°C). In Sonoma, the average low-temperature is 54.7°F (12.6°C).

Heat index

In September, the average heat index is estimated at 83.1°F (28.4°C). Constant exposure and activity lead to possible fatigue. Prolonged exercise may result in heat cramps.
Take into consideration that the heat index values are calculated for shade and light wind conditions. 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', 'feels like', 'real feel', or 'apparent temperature', is a measure that combines air temperature and relative humidity into a single value that indicates how hot the weather feels. Additional factors like clothing, differences in body mass, height, and shape, metabolic differences, and activity influence one's weather impression. Be aware that direct exposure to sunlight increases heat impact and may raise the heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are especially crucial for babies and toddlers. 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

The least humid month is September, with an average relative humidity of 59%.

Rainfall

In Sonoma, during 2.4 rainfall days, 0.08" (2mm) of precipitation is typically accumulated. In Sonoma, during the entire year, the rain falls for 73.3 days and collects up to 15.47" (393mm) of precipitation.

Daylight

In September, the average length of the day is 12h and 25min.
On the first day of the month, sunrise is at 6:39 am and sunset at 7:39 pm. On the last day of September, sunrise is at 7:04 am and sunset at 6:54 pm PDT.

Sunshine

In September, the average sunshine in Sonoma is 11h.

UV index

In Sonoma, the average daily maximum UV index in September is 5. A UV Index reading of 3 to 5 represents a moderate health risk from exposure to the Sun's UV radiation for the ordinary person.
Note: The average daily UV index of 5 in September transform into the following instructions:
Take precautions - Protection against skin and eye damage is obliged. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects.
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FAQ

What is the temperature in September in Sonoma?

In September, in Sonoma, California, the average high-temperature is 81.1°F (27.3°C), and the average low-temperature is 54.7°F (12.6°C). The average heat index (a.k.a. 'apparent temperature', 'real feel'), which combines air temperature and relative humidity, in September is estimated at 83.1°F (28.4°C).

What is the least humid month in Sonoma?

With an average relative humidity of 59%, September is the least humid month in Sonoma, California.

What is the average humidity in September in Sonoma?

In September, the average relative humidity is 59%.

How much does it rain in Sonoma in September?

In Sonoma, California, during September, the rain falls for 2.4 days and regularly aggregates up to 0.08" (2mm) of precipitation.

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

In Sonoma, California, the average day length in September is 12h and 25min.

When are sunrise and sunset in September in Sonoma?

On the first day of September in Sonoma, sunrise is at 6:39 am and sunset at 7:39 pm. On the last day of the month, sunrise is at 7:04 am and sunset at 6:54 pm PDT.

How long on average sun shines in September in Sonoma?

The average sunshine duration in September in Sonoma is 11h.

How high is the UV index in September in Sonoma?

In Sonoma, the average daily maximum UV index in September is 5. A UV Index of 3 to 5 symbolizes a moderate health threat from unprotected exposure to UV radiation.

Average temperature in September
Sonoma, CA

Average temperature in September - Sonoma, CA
  • Average high temperature in September: 81.1°F

The warmest month (with the highest average high temperature) is August (82.9°F).
The month with the lowest average high temperature is December (55°F).

  • Average low temperature in September: 54.7°F

The month with the highest average low temperature is August (54.9°F).
The coldest month (with the lowest average low temperature) is December (41.4°F).

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Average pressure in September
Sonoma, CA

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

The month with the highest atmospheric pressure is January (30.13").
The month with the lowest atmospheric pressure is June (29.91").

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Average wind speed in September
Sonoma, CA

Average wind speed in September - Sonoma, CA
  • Average wind speed in September: 4.8mph

The windiest month (with the highest average wind speed) is May (6.2mph).
The calmest month (with the lowest average wind speed) is November (4.4mph).

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Average humidity in September
Sonoma, CA

Average humidity in September - Sonoma, CA
  • Average humidity in September: 59%

The month with the highest relative humidity is March (76%).
The month with the lowest relative humidity is September (59%).

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Average rainfall in September
Sonoma, CA

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

The wettest month (with the highest rainfall) is February (3.43").
The driest months (with the least rainfall) are July and August (0.04").

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Average rainfall days in September
Sonoma, CA

Average rainfall days in September - Sonoma, CA
  • Average rainfall days in September: 2.4 days

The month with the highest number of rainy days is March (13.4 days).
The month with the least rainy days is August (0.8 days).

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

Average daylight in September / Average sunshine in September - Sonoma, CA
  • Average daylight in September: 12h and 25min

The month with the longest days is June (Average daylight: 14h and 47min).
The month with the shortest days is December (Average daylight: 9h and 33min).

  • Average sunshine in September: 11h

The month with the most sunshine is July (Average sunshine: 12h).
The month with the least sunshine is December (Average sunshine: 5.6h).

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Average sunshine days in September
Sonoma, CA

Average sunshine days in September - Sonoma, CA
  • Average sunshine days in September: 26.7 days

The month with the most sunshine days is July (28.7 days).
The month with the least sunshine days is March (16.1 days).

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Average UV index in September
Sonoma, CA

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

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

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Average cloud cover in September
Sonoma, CA

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

The month with the most cloud cover is March (Cloud cover 40).
The month with the least cloud cover is July (Cloud cover 8).

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Average visibility in September
Sonoma, CA

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

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

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