San Mateo County (San Mateo)
September
Weather in San Mateo County, California for September 2026
Your guide to San Mateo County weather in September - trends and predictions
So far, September 2026 in San Mateo County shows a warmer trend than usual by 2.5 °F.
The forecast for the upcoming days in San Mateo County predicts a temperature of 23.6 °F, which is slightly above the historical average.
In general, the average temperature in San Mateo County at the beginning of September is 21.7 °F. As the month progressed, temperatures tended to moderately rise, reaching an average of 22.3 °F by the end of September.
Precipitation in San Mateo County during September is a rare event, with an average of fewer than 2 rainy days.
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Temperatures
Rain 🌧️
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29
Dry days
1
Rainy days
0
Snow days
20°/14°
Temperatures
16 km/h
Avg max wind
81 %
Avg humidity
San Mateo County Weather September
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Temperatures trend during September in San Mateo County
See the weather trend as well as the moving average line
September weather in San Mateo County day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Cloudy | 20° /13° | 0.9 mm | 4 | |
| Sept. 2 |  Sunny | 20° /13° | 0 mm | 6 | |
| Sept. 3 | Sunny | 22° /13° | 0.2 mm | 5 | |
| Sept. 4 | Sunny | 23° /13° | 0 mm | 6 | |
| Sept. 5 | Sunny | 22° /13° | 0 mm | 6 | |
| Sept. 6 |  Overcast | 21° /12° | 0 mm | 6 | |
| Sept. 7 | Cloudy | 24° /12° | 0 mm | 6 | |
| Sept. 8 | Cloudy | 24° /12° | 0 mm | 5 | |
| Sept. 9 | Overcast | 23° /15° | 0 mm | 3 | |
| Sept. 10 | Overcast | 21° /14° | 0 mm | 5 | |
| Sept. 11 | Sunny | 19° /13° | 0 mm | 6 | |
| Sept. 12 | Sunny | 20° /13° | 0 mm | 6 | |
| Sept. 13 | Overcast | 19° /13° | 0 mm | 6 | |
| Sept. 14 | Sunny | 21° /13° | 0 mm | 5 | |
| Sept. 15 | Cloudy | 21° /13° | 0 mm | 6 | |
| Sept. 16 | Overcast | 20° /12° | 0.1 mm | 5 | |
| Sept. 17 | Overcast | 20° /12° | 0.1 mm | 5 | |
| Sept. 18 |  Patchy rain possible | 19° /13° | 12 mm | 5 | |
| Sept. 19 | Overcast | 20° /13° | 0 mm | 5 | |
| Sept. 20 | Overcast | 19° /13° | 0 mm | 3 | |
| Sept. 21 | Sunny | 20° /13° | 0 mm | 6.4 | |
| Sept. 22 | Sunny | 22° /12° | 0 mm | 6.4 | |
| Sept. 23 | Sunny | 25° /12° | 0 mm | 6.7 | |
| Sept. 24 | Sunny | 24° /14° | 0 mm | 6.4 | |
| Sept. 25 | Sunny | 22° /12° | 0 mm | 6.3 | |
| Sept. 26 | Overcast | 22° /12° | 0 mm | 6 | |
| Sept. 27 | Sunny | 19° /11° | 0 mm | 5 | |
| Sept. 28 | Sunny | 21° /12° | 0 mm | 6 | |
| Sept. 29 | Sunny | 23° /12° | 0 mm | 6 | |
| Sept. 30 | Sunny | 25° /13° | 0 mm | 6 | |
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Important Notice
Our weather forecast for San Mateo County in September is based on the analysis of historical data rather than real-time forecast models. While this provides a general overview, weather conditions can change. We recommend that you check the San Mateo County forecast closer to your planned date for the most up-to-date weather information.
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San Mateo County in September - FAQ
What are the expected maximum and minimum temperatures in San Mateo County during September?
Enjoy moderate daytime temperatures of up to 20° and cooler nights around 14°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in San Mateo County during September?
Expect minimal rainfall in San Mateo County during September, with a total of 18.2 mm over approximately 1 days. This minimal precipitation is unlikely to significantly impact plans.
What are the typical wind conditions in San Mateo County during September?
The average wind speed in San Mateo County during September is 16 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in San Mateo County
Explore the daily rainfall trends and prepare for San Mateo Countys September weather 💧
Typically, San Mateo County has 1 rainy days in September with a total of 18.2 mm of rainfall.
UV exposure in San Mateo County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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Where is San Mateo County?Get accurate weather forecasts for San Mateo County, located at latitude 37.563 and longitude -122.326. Stay updated with localized weather information tailored for San Mateo County.
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