September weather forecast
Sunnyvale, CA

The perfect blue sky, trees, buildings, and cute water fountain all reflected in the calm pool of water with birds in Sunnyvale, California
The perfect blue sky, trees, buildings, and cute water fountain all reflected in the calm pool of water with birds in Sunnyvale, California

Weather in September

September, the first month of the autumn in Sunnyvale, is still a warm month, with an average temperature fluctuating between 77.9°F (25.5°C) and 55.9°F (13.3°C).

Temperature

In September, the average high-temperature is relatively the same as in August - a still warm 77.9°F (25.5°C). In September, the average low-temperature is 55.9°F (13.3°C).

Humidity

The months with the lowest humidity in Sunnyvale are September and October, with an average relative humidity of 63%.

Rainfall

In September, the rain falls for 2.2 days. Throughout September, 0.08" (2mm) of precipitation is accumulated. In Sunnyvale, during the entire year, the rain falls for 50 days and collects up to 3.9" (99mm) of precipitation.

Daylight

In September, the average length of the day in Sunnyvale, California, is 12h and 25min.
On the first day of September in Sunnyvale, sunrise is at 6:38 am and sunset at 7:37 pm. On the last day of the month, sunrise is at 7:03 am and sunset at 6:53 pm PDT.

Sunshine

In September, the average sunshine is 11.1h.

UV index

The average daily maximum UV index in September in Sunnyvale is 5. A UV Index of 3 to 5 symbolizes a medium health hazard from exposure to the Sun's UV rays 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 Sun's most intense and consequently most harmful UV radiation during midday hours should be decreased by minimizing exposure and seeking shade. A wide-brim hat offers excellent sun protection for the 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 least humid month in Sunnyvale?

September and October, with an average relative humidity of 63%, are the least humid months in Sunnyvale.

What is the average humidity in September in Sunnyvale?

In September, the average relative humidity in Sunnyvale is 63%.

How much does it rain in Sunnyvale in September?

In Sunnyvale, California, in September, during 2.2 rainfall days, 0.08" (2mm) of precipitation is typically accumulated.

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

The average day length in September in Sunnyvale is 12h and 25min.

When is the sunrise / sunset in September in Sunnyvale?

In September, on the first day of the month, sunrise is at 6:38 am and sunset at 7:37 pm. On the last day of the month, in Sunnyvale, California, sunrise is at 7:03 am and sunset at 6:53 pm PDT.

How long on average sun shines in September in Sunnyvale?

In Sunnyvale, the average sunshine duration in September is 11.1h.

What is the UV index intensity in September in Sunnyvale?

In Sunnyvale, California, the average daily maximum UV index in September is 5. A UV Index reading of 3 to 5 represents a medium hazard to health from unsafe exposure to Sun's UV rays.

Average temperature in September
Sunnyvale, CA

Average temperature in September - Sunnyvale, CA
  • Average high temperature in September: 77.9°F

The warmest month (with the highest average high temperature) is July (79.9°F).
The month with the lowest average high temperature is December (56.8°F).

  • Average low temperature in September: 55.9°F

The month with the highest average low temperature is August (56.8°F).
The coldest months (with the lowest average low temperature) are February and December (44.2°F).

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Average pressure in September
Sunnyvale, CA

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

The month with the highest atmospheric pressure is January (30.13").
The months with the lowest atmospheric pressure are June and September (29.92").

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Average wind speed in September
Sunnyvale, CA

Average wind speed in September - Sunnyvale, CA
  • Average wind speed in September: 4.6mph

The windiest month (with the highest average wind speed) is April (6.2mph).
The calmest month (with the lowest average wind speed) is September (4.6mph).

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Average humidity in September
Sunnyvale, CA

Average humidity in September - Sunnyvale, CA
  • Average humidity in September: 63%

The month with the highest relative humidity is March (73%).
The months with the lowest relative humidity are September and October (63%).

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Average rainfall in September
Sunnyvale, CA

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

The wettest months (with the highest rainfall) are February and March (0.75").
The driest month (with the least rainfall) is July (0").

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Average rainfall days in September
Sunnyvale, CA

Average rainfall days in September - Sunnyvale, CA
  • Average rainfall days in September: 2.2 days

The month with the highest number of rainy days is March (9.6 days).
The month with the least rainy days is August (0.4 days).

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

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

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 38min).

  • 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: 5.9h).

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Average sunshine days in September
Sunnyvale, CA

Average sunshine days in September - Sunnyvale, CA
  • Average sunshine days in September: 27.5 days

The month with the most sunshine days is August (30.1 days).
The month with the least sunshine days is March (19.9 days).

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Average UV index in September
Sunnyvale, CA

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

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

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Average cloud cover in September
Sunnyvale, CA

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

The month with the most cloud cover is March (Cloud cover 35).
The month with the least cloud cover is July (Cloud cover 7).

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Average visibility in September
Sunnyvale, CA

Average visibility in September - Sunnyvale, 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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