Sunnyvale weather in September: Sunnyvale, California: normal highs, lows, rain and records for September
Sunnyvale in September has a normal high of 78°F and a normal low of 57°F, a daily mean of 68°F, holding near 78°F all month. Measurable precipitation falls on 1 days in a normal September, 0.07 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 25°C and low of 14°C, 2 mm of precipitation in September.
- NOAA stationMoffett Federal Airfield
- Station IDUSW00023244
- Location37.41°N 122.05°W
- Elevation39 ft (12 m)
- From the center2 miles
- Population156,792
- Jan 59° 42°
- Feb 62° 45°
- Mar 65° 47°
- Apr 68° 49°
- May 72° 53°
- Jun 76° 56°
- Jul 77° 59°
- Aug 77° 59°
- Sep 78° 57°
- Oct 74° 53°
- Nov 66° 46°
- Dec 59° 42°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is Sunnyvale in September?
The normal high is 78°F and the normal low 57°F, for a daily mean of 67.5°F. September is 0.5°F cooler than August and 3.9°F warmer than October. September is the 3rd warmest month of the year in Sunnyvale and the 10th wettest. Across the month the normal high falls 1°F, from 78°F on September 1 to 77°F on September 30. From one year to the next September's mean temperature typically moves about 1.9°F either way (NOAA's standard deviation), so roughly two Septembers in three average between 66°F and 69°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 6%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| September 1 | 78°F | 58°F | 1% | 0% |
| September 8 | 78°F | 58°F | 2% | 0% |
| September 15 | 78°F | 57°F | 3% | 1% |
| September 22 | 78°F | 57°F | 4% | 1% |
| September 30 | 77°F | 56°F | 6% | 2% |
Every day of September: normal high, low and chance of precipitation (warmest afternoon September 4, coldest night September 30)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| September 1 | 78°F | 58°F | 1% | 0% | 13 h |
| September 2 | 78°F | 58°F | 1% | 0% | 13 h |
| September 3 | 78°F | 58°F | 1% | 0% | 13 h |
| September 4 | 78°F | 58°F | 1% | 0% | 12 h 50 min |
| September 5 | 78°F | 58°F | 1% | 0% | 12 h 50 min |
| September 6 | 78°F | 58°F | 2% | 0% | 12 h 50 min |
| September 7 | 78°F | 58°F | 2% | 0% | 12 h 50 min |
| September 8 | 78°F | 58°F | 2% | 0% | 12 h 50 min |
| September 9 | 78°F | 58°F | 2% | 0% | 12 h 40 min |
| September 10 | 78°F | 58°F | 2% | 1% | 12 h 40 min |
| September 11 | 78°F | 58°F | 2% | 1% | 12 h 40 min |
| September 12 | 78°F | 58°F | 2% | 1% | 12 h 40 min |
| September 13 | 78°F | 58°F | 2% | 1% | 12 h 30 min |
| September 14 | 78°F | 58°F | 3% | 1% | 12 h 30 min |
| September 15 | 78°F | 57°F | 3% | 1% | 12 h 30 min |
| September 16 | 78°F | 57°F | 3% | 1% | 12 h 30 min |
| September 17 | 78°F | 57°F | 3% | 1% | 12 h 20 min |
| September 18 | 78°F | 57°F | 3% | 1% | 12 h 20 min |
| September 19 | 78°F | 57°F | 4% | 1% | 12 h 20 min |
| September 20 | 78°F | 57°F | 4% | 1% | 12 h 20 min |
| September 21 | 78°F | 57°F | 4% | 1% | 12 h 10 min |
| September 22 | 78°F | 57°F | 4% | 1% | 12 h 10 min |
| September 23 | 78°F | 57°F | 4% | 1% | 12 h 10 min |
| September 24 | 77°F | 57°F | 5% | 1% | 12 h 10 min |
| September 25 | 77°F | 57°F | 5% | 2% | 12 h 10 min |
| September 26 | 77°F | 56°F | 5% | 2% | 12 h |
| September 27 | 77°F | 56°F | 5% | 2% | 12 h |
| September 28 | 77°F | 56°F | 6% | 2% | 12 h |
| September 29 | 77°F | 56°F | 6% | 2% | 12 h |
| September 30 | 77°F | 56°F | 6% | 2% | 11 h 50 min |
- Normal high
- 78°FSeptember average
- Normal low
- 57°FSeptember average
- Precipitation
- 0.07 inmonth total
- Days with precipitation
- 10.01 inch or more
- Days at 90°F or more
- 3
- Daylight
- 13 h to 11 h 50 minSeptember 1 to September 30
- Days at 70°F or more
- 28
- Days at 80°F or more
- 10
- Sunshine
- 82%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USW00023244; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Sunnyvale in September?
On a given September day the chance of 0.01 inch or more is 3% on average, highest around September 30 (6%). In all, 0.07 in falls on 1 days of a normal September.
In a normal September in Sunnyvale, 3 days reach 90°F.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USW00023244.
What are the records for September in Sunnyvale?
The warmest September temperature on this station's record (since 1945) is 106°F, on September 2, 2017; the coldest is 41°F, on September 12, 1946. The wettest September brought 1.98 in (1959).
The September mean against the 1991-2020 normal of 67.5°F: 2025 70.1°F (+2.6), 2026 67.5°F (at normal). 1 of 2 ran warmer than normal.
| September | Mean | Against normal | Precip. |
|---|---|---|---|
| 2025 | 70.1°F | +2.6°F | – |
| 2026 | 67.5°F | at normal | – |
Source: records: ACIS, station USW00023244; recent months: ACIS, station USW00023244. Records and recent months use complete months only.
How does September in Sunnyvale compare across California?
Across the 219 places PlainClimate covers in California, September normal highs run from 64°F in Eureka to 104°F in Brawley; Sunnyvale's is 78°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.
Other months and places
- Sunnyvale in August77°F by day, 59°F at night
- Sunnyvale in October74°F by day, 53°F at night
- Sunnyvale through the yearEvery month, frost dates, records and recent years
- California in SeptemberThe statewide normal and the warmest and coolest places
- Brawley: California's warmest Septembernormal high 104°F