Millbrae Weather in September
Average highs run from 75°F on September 1 to 75°F on September 30, and lows from 56°F to 55°F. Normal precipitation for the month is 0.07 in over about 1 wet days.
September day by day
The normal high and low for each date, and the record, in °F.
- Normal low
- Normal high
- Record high
- Record low
September at a glance
- Average high
- 75°F
- Average low
- 56°F
- Precipitation
- 0.07 in
- Record high
- 104°FSep 1, 2017
- Record low
- 41°FSep 30, 1950
- Chance of a freeze
- 0%
- Days of 90°F or more
- 1.6
- Daylight
- 12 h 58 min to 11 h 50 min
- Cloud cover
- 51%
- Humidity
- 83%
- Dew point
- 55°F
- Wind
- 8.3 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation.
| Date | Normal high | Normal low | Record high | Record low | Chance wet |
|---|---|---|---|---|---|
| Sep 1 | 75°F | 56°F | 104°F 2017 | 49°F 1957 | 2% |
| Sep 2 | 75°F | 56°F | 104°F 2017 | 49°F 1946 | 2% |
| Sep 3 | 75°F | 56°F | 93°F 1961 | 50°F 1945 | 2% |
| Sep 4 | 75°F | 56°F | 92°F 1961 | 50°F 1947 | 2% |
| Sep 5 | 75°F | 56°F | 97°F 2022 | 45°F 1954 | 2% |
| Sep 6 | 75°F | 56°F | 102°F 2020 | 47°F 1950 | 2% |
| Sep 7 | 75°F | 56°F | 97°F 2020 | 50°F 1960 | 2% |
| Sep 8 | 75°F | 56°F | 100°F 1984 | 48°F 1946 | 2% |
| Sep 9 | 75°F | 56°F | 94°F 2026 | 46°F 1946 | 2% |
| Sep 10 | 75°F | 56°F | 94°F 1979 | 49°F 1947 | 2% |
| Sep 11 | 75°F | 56°F | 98°F 1979 | 49°F 1951 | 3% |
| Sep 12 | 75°F | 56°F | 100°F 1979 | 47°F 1946 | 3% |
| Sep 13 | 75°F | 56°F | 101°F 1971 | 47°F 1947 | 3% |
| Sep 14 | 75°F | 56°F | 103°F 1971 | 46°F 1947 | 3% |
| Sep 15 | 75°F | 56°F | 98°F 1971 | 48°F 1970 | 3% |
| Sep 16 | 75°F | 56°F | 90°F 1968 | 49°F 2006 | 3% |
| Sep 17 | 75°F | 56°F | 94°F 1984 | 50°F 1945 | 3% |
| Sep 18 | 75°F | 56°F | 93°F 2009 | 46°F 1955 | 4% |
| Sep 19 | 75°F | 56°F | 93°F 2000 | 46°F 1947 | 4% |
| Sep 20 | 75°F | 56°F | 93°F 1983 | 48°F 1947 | 4% |
| Sep 21 | 75°F | 56°F | 95°F 2003 | 45°F 1955 | 4% |
| Sep 22 | 75°F | 56°F | 91°F 1946 | 48°F 1981 | 4% |
| Sep 23 | 75°F | 56°F | 92°F 1978 | 45°F 1972 | 5% |
| Sep 24 | 75°F | 56°F | 94°F 2019 | 48°F 1945 | 5% |
| Sep 25 | 75°F | 56°F | 96°F 2019 | 47°F 1948 | 5% |
| Sep 26 | 75°F | 56°F | 95°F 1958 | 46°F 1948 | 5% |
| Sep 27 | 75°F | 55°F | 96°F 1958 | 47°F 1948 | 5% |
| Sep 28 | 75°F | 55°F | 96°F 2020 | 47°F 1947 | 5% |
| Sep 29 | 75°F | 55°F | 95°F 2020 | 45°F 1950 | 6% |
| Sep 30 | 75°F | 55°F | 94°F 1980 | 41°F 1950 | 6% |
Chance of rain
- Chance of a wet day
Sunrise and sunset
Times for 2026, local time (PDT).
- September 1
- sunrise 6:40 AM, sunset 7:38 PM
- September 30
- sunrise 7:04 AM, sunset 6:54 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USW00023234 (San Francisco Intl AP), public domain. Records: NOAA GHCN-Daily, station USW00023234, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.