Sonoma
California, USA
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
Sonoma, CA

Neat rows of vines in a vineyard farm in Sonoma, California, the sun rays beaming through the cloudy sunset sky, and distant hilly silhouettes
Neat rows of vines in a vineyard farm in Sonoma, California, the sun rays beaming through the cloudy sunset sky, and distant hilly silhouettes
The first month of the autumn, September, is still a warm month in Sonoma, California, with temperature in the range of an average low of 54.7°F (12.6°C) and an average high of 81.1°F (27.3°C).

Temperature

In Sonoma, the average high-temperature is essentially the same as in August - a still moderately hot 81.1°F (27.3°C). The average low-temperature, in Sonoma, California, 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 'real feel', 'apparent temperature', 'feels like', or 'felt air temperature', is an index that combines air temperature and relative humidity to determine the human-perceived temperature equivalent. Additional factors like differences in body mass, height, and shape, wind, pregnancy, 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. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.

Humidity

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

Rainfall

In Sonoma, during 2.4 rainfall days, 0.08" (2mm) of precipitation is typically accumulated. Throughout the year, in Sonoma, there are 73.3 rainfall days, and 15.47" (393mm) of precipitation is accumulated.

Daylight

The average length of the day in Sonoma is 12.4h.

Sunshine

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

UV index

In Sonoma, California, the average daily maximum UV index is 5. A UV Index estimate of 3 to 5 represents a medium vulnerability from the exposure to the Sun's UV rays for ordinary individuals.
Note: In September, the average maximum UV index of 5 translate into the following recommendations:
Take precautions - Protection against the 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. 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.

What is the temperature in September in Sonoma?

In September, in Sonoma, the average high-temperature is 81.1°F (27.3°C), and the average low-temperature is 54.7°F (12.6°C). In September, the average heat index (a.k.a. 'feels like', 'real feel'), that takes the relative humidity and factores it into the air temperature reading, is evaluated at 83.1°F (28.4°C).

What is the least humid month in Sonoma?

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

What is the average humidity in September in Sonoma?

In Sonoma, the average relative humidity in September is 59%.

How much does it rain in Sonoma in September?

In Sonoma, California, in September, it is raining for 2.4 days, with typically 0.08" (2mm) of accumulated precipitation.

How many hours of daylight does Sonoma have in September?

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

How long on average sun shines in September in Sonoma?

The average sunshine in September in Sonoma is 11h.

What is the UV index reading in September in Sonoma?

The average daily maximum UV index in September in Sonoma, California, is 5. A UV Index estimate of 3 to 5 represents a medium hazard to health from unprotected exposure to the UV radiation.
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).

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%).

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

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

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 lowest number of rainy days is August (0.8 days).

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

The month with the longest days is June (Average daylight: 14.8h).
The month with shortest days is December (Average daylight: 9.5h).

  • Average sunshine in September: 11h

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

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

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