September weather forecast and climate
San Bruno, CA

Weather in September

September, the first month of the autumn, in San Bruno, is still a pleasant month, with average temperature ranging between max 69.8°F (21°C) and min 56.5°F (13.6°C).

Temperature

September is the warmest month, with an average high-temperature of 69.8°F (21°C) and an average low-temperature of 56.5°F (13.6°C).

Humidity

In September, the average relative humidity is 74%.

Rainfall

In San Bruno, California, during 3.1 rainfall days, 0.12" (3mm) of precipitation is typically accumulated. In San Bruno, during the entire year, the rain falls for 81.8 days and collects up to 13.46" (342mm) of precipitation.

Daylight

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

Sunshine

The average sunshine in San Bruno is 10.8h.

UV index

Months with the highest UV index are June through September, with an average maximum UV index of 5. A UV Index reading of 3 to 5 represents a moderate health risk from unprotected exposure to the Sun's UV rays for the average person.
Note: The average daily UV index of 5 in September transform into the following instructions:
Take precautions - Protection against the skin and eye damage is obliged. The Sun's most intense and consequently most harmful UV radiation during midday hours should be decreased by minimizing exposure and seeking shade. 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 warmest month in San Bruno?

With an average high-temperature of 69.8°F (21°C) and an average low-temperature of 56.5°F (13.6°C), September is the warmest month in San Bruno.

What is the temperature in September in San Bruno?

The average high-temperature, in September, in San Bruno, is 69.8°F (21°C), while the average low-temperature is 56.5°F (13.6°C).

What is the average humidity in September in San Bruno?

In September, the average relative humidity is 74%.

How much does it rain in San Bruno in September?

In San Bruno, in September, during 3.1 rainfall days, 0.12" (3mm) of precipitation is typically accumulated.

What is the average length of the day in September in San Bruno?

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

How many hours of sunshine does San Bruno have in September?

In September, the average sunshine in San Bruno, California, is 10.8h.

What are the months with the highest UV index in San Bruno?

June through September, with an average maximum UV index of 5, are months with the highest UV index in San Bruno.

What is the UV index reading in September in San Bruno?

In San Bruno, the average daily maximum UV index in September is 5. A UV Index value of 3 to 5 symbolizes a moderate health threat from the exposure to the Sun's UV rays.

Average temperature in September
San Bruno, CA

Average temperature in September - San Bruno, CA
  • Average high temperature in September: 69.8°F

The warmest month (with the highest average high temperature) is September (69.8°F).
The month with the lowest average high temperature is December (55.8°F).

  • Average low temperature in September: 56.5°F

The month with the highest average low temperature is September (56.5°F).
The coldest month (with the lowest average low temperature) is December (47.7°F).

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Average pressure in September
San Bruno, CA

Average pressure in September - San Bruno, 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 September (29.92").

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Average wind speed in September
San Bruno, CA

Average wind speed in September - San Bruno, CA
  • Average wind speed in September: 6.3mph

The windiest month (with the highest average wind speed) is April (8.5mph).
The calmest months (with the lowest average wind speed) are August and September (6.3mph).

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Average humidity in September
San Bruno, CA

Average humidity in September - San Bruno, CA
  • Average humidity in September: 74%

The month with the highest relative humidity is August (79%).
Months with the lowest relative humidity are October and November (71%).

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Average rainfall in September
San Bruno, CA

Average rainfall in September - San Bruno, CA
  • Average rainfall in September: 0.12"

The wettest month (with the highest rainfall) is February (2.72").
The driest months (with the least rainfall) are July and August (0.04").

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Average rainfall days in September
San Bruno, CA

Average rainfall days in September - San Bruno, CA
  • Average rainfall days in September: 3.1 days

The month with the highest number of rainy days is March (13.3 days).
Months with the least rainy days are July and August (2.2 days).

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Average daylight in September /
Average sunshine in September
San Bruno, CA

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

The month with the longest days is June (Average daylight: 14.7h).
The month with the shortest days is December (Average daylight: 9.6h).

  • Average sunshine in September: 10.8h

The month with the most sunshine is July (Average sunshine: 11.8h).
The month with the least sunshine is December (Average sunshine: 5.8h).

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Average sunshine days in September
San Bruno, CA

Average sunshine days in September - San Bruno, CA
  • Average sunshine days in September: 25.2 days

The month with the most sunshine days is July (27.3 days).
The month with the least sunshine days is March (16.3 days).

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Average UV index in September
San Bruno, CA

Average UV index in September - San Bruno, CA
  • Average UV index in September: 5

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

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Average cloud cover in September
San Bruno, CA

Average cloud cover in September - San Bruno, CA
  • Average cloud cover in September: 16

The month with the most cloud cover is March (Cloud cover 37).
The month with the least cloud cover is September (Cloud cover 16).

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Average visibility in September
San Bruno, CA

Average visibility in September - San Bruno, 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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