September weather forecast
San Bruno, CA

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Weather in September

The first month of the autumn, September, is still a pleasant month in San Bruno, California, with temperature in the range of an average high of 69.8°F (21°C) and an average low of 56.5°F (13.6°C).

Temperature

In San Bruno, September is the warmest month, with temperatures averaging a high of 69.8°F (21°C) and a low of 56.5°F (13.6°C).

Humidity

In San Bruno, the average relative humidity in September is 74%.

Rainfall

In San Bruno, in September, it is raining for 3.1 days, with typically 0.12" (3mm) of accumulated precipitation. Throughout the year, there are 81.8 rainfall days, and 13.46" (342mm) of precipitation is accumulated.

Daylight

In San Bruno, the average length of the day in September is 12h and 25min.
On the first day of September in San Bruno, sunrise is at 6:40 am and sunset at 7:38 pm. On the last day of the month, sunrise is at 7:05 am and sunset at 6:53 pm PDT.

Sunshine

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

UV index

The months with the highest UV index are June through September, with an average maximum UV index of 5. A UV Index value of 3 to 5 symbolizes a moderate health risk from unprotected exposure to Sun's UV rays for the ordinary person.
Note: In September, the maximum UV index of 5 suggests this advice:
Prioritize safety - The need to safeguard skin and eyes from harm is emphasized. Considering the Sun's intensity during midday, it's wise to minimize direct exposure. Wearing a wide-brim hat can block approximately 50% of UV radiation, protecting the eyes.
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Frequently asked questions

What part of the year is the hottest in San Bruno?

San Bruno witnesses the warmest weather in September, with temperatures averaging a high of 69.8°F (21°C) and a low of 56.5°F (13.6°C).

What are September temperatures in San Bruno?

In September, in San Bruno, the average high-temperature is 69.8°F (21°C), and 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 in San Bruno, California, is 74%.

How many days does it rain in September in San Bruno?

In San Bruno, California, 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 day length in September in San Bruno, California, is 12h and 25min.

What time are sunrise and sunset in September in San Bruno?

In September, on the first day of the month, sunrise is at 6:40 am and sunset at 7:38 pm. On the last day of the month, in San Bruno, sunrise is at 7:05 am and sunset at 6:53 pm PDT.

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

In September, the average sunshine duration is 10.8h.

When is 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, California.

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

The average daily maximum UV index in September in San Bruno, California, is 5. A UV Index estimate of 3 to 5 represents a moderate health threat from exposure to Sun's UV rays.
Average humidity
Average rainfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

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"Hg

The month with the highest atmospheric pressure is January (30.13"Hg).
The month with the lowest atmospheric pressure is September (29.92"Hg).

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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%).
The 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).
The 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: 12h and 2min

The month with the longest days is June (Average daylight: 14h and 42min).
The month with the shortest days is December (Average daylight: 9h and 36min).

  • Average sunshine in September: 10h and 5min

The month with the most sunshine is July (Average sunshine: 11h and 48min).
The month with the least sunshine is December (Average sunshine: 5h and 48min).

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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

The months with the highest UV index are June, July, August and September (UV index 5).
The 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

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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San Bruno, California, USA

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