September weather forecast and climate
Redwood City, CA

The intricate design of the organized Redwood City in California, with a scenic view of the harbor and the rest of the city
The intricate design of the organized Redwood City in California, with a scenic view of the harbor and the rest of the city

Weather in September

The first month of the autumn, September, is still a pleasant month in Redwood City, California, with average temperature varying between 56.7°F (13.7°C) and 72.7°F (22.6°C).

Temperature

In September, the average high-temperature is relatively the same as in August - a still pleasant 72.7°F (22.6°C). The average low-temperature, in September, is 56.7°F (13.7°C).

Humidity

In September, the average relative humidity in Redwood City, California, is 69%.

Rainfall

In September, in Redwood City, the rain falls for 2.4 days. Throughout September, 0.12" (3mm) of precipitation is accumulated. In Redwood City, during the entire year, the rain falls for 73.4 days and collects up to 11.89" (302mm) of precipitation.

Ocean temperature

August and September, with an average ocean temperature of 57.7°F (14.3°C), are months with the warmest seawater in Redwood City.
Note: Swimming in 57.7°F (14.3°C) is considered dangerous. Unprotected immersion in temperatures below 50°F (10°C) causes quickly maximum intensity cold shock with hyperventilation.

Daylight

In Redwood City, the average length of the day is 12.4h.

Sunshine

In Redwood City, the average sunshine in September is 11h.

UV index

Months with the highest UV index in Redwood City are June through September, with an average maximum UV index of 5. A UV Index value of 3 to 5 symbolizes a medium vulnerability from the exposure to the Sun's UV rays for the ordinary person.
Note: The daily maximum UV index of 5 interpret into the following advice:
Take precautions - Protection against sun damage is advised. 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.
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FAQ

What is the average humidity in September in Redwood City?

The average relative humidity in September is 69%.

How many days does it rain in September in Redwood City?

In Redwood City, California, in September, during 2.4 rainfall days, 0.12" (3mm) of precipitation is typically accumulated.

What are the months with the warmest ocean in Redwood City?

Months with the warmest seawater are August and September, with an average ocean temperature of 57.7°F (14.3°C).

How cold is the water in September in Redwood City?

In September, the average ocean temperature is 57.7°F (14.3°C). Swimming in 57.7°F (14.3°C) is considered life-threatening. Even a few minutes in 55.4°F (13°C) water is uncomfortable, and swimming below 50°F (10°C) may cause total loss of breathing control and cold shock, depending on a person's physique.

How many hours of daylight does Redwood City have in September?

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

How many hours of sunshine does Redwood City have in September?

The average sunshine in September is 11h.

When is the highest UV index in Redwood City?

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

How high is the UV index in September in Redwood City?

In September, the average daily maximum UV index in Redwood City is 5. A UV Index of 3 to 5 symbolizes a medium health risk from the exposure to the Sun's UV radiation.

Average temperature in September
Redwood City, CA

Average temperature in September - Redwood City, CA
  • Average high temperature in September: 72.7°F

The warmest months (with the highest average high temperature) are July and August (73°F).
The month with the lowest average high temperature is December (55.9°F).

  • Average low temperature in September: 56.7°F

The month with the highest average low temperature is September (56.7°F).
The coldest month (with the lowest average low temperature) is February (46°F).

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Average pressure in September
Redwood City, CA

Average pressure in September - Redwood City, 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
Redwood City, CA

Average wind speed in September - Redwood City, CA
  • Average wind speed in September: 5.5mph

The windiest month (with the highest average wind speed) is April (7.5mph).
The calmest months (with the lowest average wind speed) are August, September and October (5.5mph).

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Average humidity in September
Redwood City, CA

Average humidity in September - Redwood City, CA
  • Average humidity in September: 69%

The month with the highest relative humidity is March (75%).
The month with the lowest relative humidity is October (68%).

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Average rainfall in September
Redwood City, CA

Average rainfall in September - Redwood City, CA
  • Average rainfall in September: 0.12"

The wettest month (with the highest rainfall) is February (2.36").
The driest months (with the least rainfall) are July and August (0.04").

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Average rainfall days in September
Redwood City, CA

Average rainfall days in September - Redwood City, CA
  • Average rainfall days in September: 2.4 days

The month with the highest number of rainy days is March (12.8 days).
The month with the least rainy days is August (0.8 days).

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Average sea temperature in September
Redwood City, CA

Average sea temperature in September - Redwood City, CA
  • Average sea temperature in September: 57.7°F

The best months for swimming (with the highest average sea temperature) are August and September (57.7°F).
The coldest month (with the lowest average sea temperature) is April (53.4°F).

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Average daylight in September /
Average sunshine in September
Redwood City, CA

Average daylight in September / Average sunshine in September - Redwood City, 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: 11h

The month with the most sunshine is July (Average sunshine: 12h).
The month with the least sunshine is December (Average sunshine: 5.8h).

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Average sunshine days in September
Redwood City, CA

Average sunshine days in September - Redwood City, CA
  • Average sunshine days in September: 26.4 days

The month with the most sunshine days is August (27.6 days).
The month with the least sunshine days is March (17.5 days).

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Average UV index in September
Redwood City, CA

Average UV index in September - Redwood City, 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 November and December (UV index 3).

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Average cloud cover in September
Redwood City, CA

Average cloud cover in September - Redwood City, CA
  • Average cloud cover in September: 12

The month with the most cloud cover is March (Cloud cover 35).
The month with the least cloud cover is July (Cloud cover 9).

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Average visibility in September
Redwood City, CA

Average visibility in September - Redwood City, 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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