Sunnyvale, CA weather in September
Sunnyvale is mild and dry in September: highs average 78°F and nights drop to about 57°F. Expect about 1 wet day. This is the peak of the warm season in Sunnyvale. A great month for outdoor plans.
- Normal high
- 78°F
- Normal low
- 57°F
- Wet days
- 1
- 0.07 in total
- Muggy days
- 0
- dew point 65°F+
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 78°F | 77°F |
| Normal low | 58°F | 56°F |
| Chance of a wet day | 1% | 6% |
| Sunrise / sunset | 6:38 am / 7:37 pm | 7:02 am / 6:53 pm |
| Daylight | 13.0 h | 11.8 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Pacific Time).
A typical September day
- 6 am58°Fdew point 53°F
- 9 am64°Fdew point 55°F
- Noon70°Fdew point 55°F
- 3 pm71°Fdew point 53°F
- 6 pm64°Fdew point 53°F
- 9 pm61°Fdew point 53°F
NOAA hourly normals (local standard time) from San Francisco Intl Airport (25 mi away); average wind 11 mph; clear or few clouds in 64% of daytime hours, mostly cloudy or overcast in 20%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F21 of 30
- Hot dayshigh 90°F or more3 of 30
- Muggy daysdaily mean dew point 65°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow1 of 30
- Notable rainat least 0.10 in0 of 30
- Freezing nightslow 32°F or below0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain in September
Normal precipitation is 0.07 in; a dry September brings about 0.0 in and a wet one about 0.06 in (25th and 75th percentiles). Days with half an inch or more are rare.
How September varies from year to year
- Warmest September, 1991-20202017: average high 83°F
- Coolest September2012: average high 74°F
- Wettest September2013: 0.5 in
- Driest September1992: no measurable precipitation
- Highest reading106°F (September 2, 2017)
- Lowest reading48°F (September 30, 2007)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 77°F | 78°F | 74°F |
| Normal low | 59°F | 57°F | 53°F |
| Wet days | 0 | 1 | 4 |
| Comfortable days | 23 | 21 | 23 |
| Daylight | 13.6 h | 12.4 h | 11.2 h |
Highs change by +1°F from August and -4°F into October.
Nearby alternatives in September
- Warmer: Concord, CA42 mi · high 84°F · 1 wet day
- Cooler: San Francisco, CA35 mi · high 70°F · 1 wet day
How Sunnyvale ranks in September
- Normal high228th warmest of 378 cities; 46th of 60 in California
- Wet days38th driest of 378
- Comfortable days16th most of 342
Heating and cooling
September has 18 heating degree days and 93 cooling degree days (base 65°F), 4% of the year's total heating and cooling demand.
Questions
How hot is Sunnyvale in September?
The normal high is 78°F and the normal low is 57°F. From 1991 to 2020 the hottest September reading was 106°F (most recently on September 2, 2017).
Does it rain a lot in Sunnyvale in September?
About 1 days in September have at least 0.01 in of precipitation, and the normal total is 0.07 in. The wettest September in 1991-2020 was in 2013 (0.5 in); the driest was in 1992, with no measurable precipitation.
Is September a good time to visit Sunnyvale?
September ranks 5th of 12 months on our comfort score for Sunnyvale (79 out of 100). It has about 21 comfortable days and about 3 days at 90°F or hotter. The best months are May, June and July.
Where the numbers come from
- Temperature, rain and frost dates: Moffett Federal Airfield (USW00023244), 2.6 mi NNW of the city center, 39 ft (85 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Snowfall: Palo Alto (USC00046646), 7.7 mi NW of the city center, 25 ft (99 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Snow depth: Newark (USC00046144), 10 mi N of the city center, 10 ft (114 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Humidity and wind by hour and cloud cover: San Francisco Intl Airport (USW00023234), 25 mi NW of the city center, 8 ft (116 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: N Y. Mineta Sn Jo Intl Apt (724945-23293), 6.2 mi E of the city center, 49 ft (75 ft lower than the city). Hourly observations, 1991-2020.