San Mateo County (San Mateo)
September
Weather in San Mateo County, California for September 2025
Your guide to San Mateo County weather in September - trends and predictions
In general, the average temperature in San Mateo County at the beginning of September is 21.3 °F. As the month progressed, temperatures tended to slightly increase, reaching an average of 21.4 °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.
New! Chat with our AI weatherman - it’s amazing and free.
Temperatures
Rain 🌧️
More
29
Dry days
1
Rainy days
0
Snow days
20°/13°
Temperatures
17 km/h
Avg max wind
78 %
Avg humidity
San Mateo County Weather September
Move between months or click on a day
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
Click on a date for more information
| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Cloudy | 18° /13° | 0 mm | 4 | |
| Sept. 2 |  Sunny | 19° /14° | 0 mm | 5 | |
| Sept. 3 | Sunny | 26° /13° | 0 mm | 7 | |
| Sept. 4 | Sunny | 24° /15° | 0 mm | 6 | |
| Sept. 5 | Sunny | 22° /15° | 0 mm | 6 | |
| Sept. 6 |  Overcast | 21° /13° | 0 mm | 5 | |
| Sept. 7 | Cloudy | 19° /12° | 0 mm | 4 | |
| Sept. 8 | Cloudy | 19° /12° | 0 mm | 4 | |
| Sept. 9 | Cloudy | 19° /12° | 0 mm | 4 | |
| Sept. 10 | Overcast | 17° /12° | 0 mm | 4 | |
| Sept. 11 | Sunny | 19° /13° | 0 mm | 5 | |
| Sept. 12 | Sunny | 19° /13° | 0 mm | 5 | |
| Sept. 13 | Overcast | 21° /13° | 0 mm | 5 | |
| Sept. 14 | Sunny | 19° /13° | 0 mm | 5 | |
| Sept. 15 | Cloudy | 17° /13° | 0 mm | 4 | |
| Sept. 16 | Overcast | 18° /12° | 0.2 mm | 4 | |
| Sept. 17 | Overcast | 16° /12° | 0 mm | 4 | |
| Sept. 18 |  Patchy rain possible | 18° /13° | 0.5 mm | 4 | |
| Sept. 19 | Overcast | 18° /12° | 0 mm | 4 | |
| Sept. 20 | Overcast | 19° /12° | 0 mm | 4 | |
| Sept. 21 | Cloudy | 20° /12° | 0 mm | 5 | |
| Sept. 22 | Cloudy | 21° /13° | 0 mm | 5 | |
| Sept. 23 |  Partly cloudy | 27° /13° | 0 mm | 7 | |
| Sept. 24 | Partly cloudy | 23° /15° | 0 mm | 6 | |
| Sept. 25 | Cloudy | 19° /13° | 0 mm | 4 | |
| Sept. 26 | Overcast | 19° /13° | 0 mm | 4 | |
| Sept. 27 | Overcast | 23° /13° | 0 mm | 5 | |
| Sept. 28 | Overcast | 18° /13° | 0 mm | 4 | |
| Sept. 29 | Overcast | 20° /12° | 0 mm | 5 | |
| Sept. 30 | Partly cloudy | 28° /12° | 0 mm | 7 | |
| Next | |||||
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.
Change Month
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 13°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in San Mateo County during September?
Rainfall in San Mateo County during September is rare to nonexistent, with the total expected rainfall being less than 10 mm and approximately 1 days seeing any precipitation. Planning without the concern for rain is generally straightforward during this very dry period.
What are the typical wind conditions in San Mateo County during September?
The average wind speed in San Mateo County during September is 17 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 💧
UV exposure in San Mateo County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
Top locations in San Mateo County
Select a location for an accurate weather forecast
More Locations Quick links
More San Mateo County weather pages
You are here
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.
Found a mistake?
We appreciate your attention to details. Tell us here.