S
M
T
W
T
F
S
30
101°
81°
31
102°
80°
1
104°
81°
2
102°
80°
3
94°
78°
4
99°
77°
5
101°
81°
6
100°
80°
7
102°
80°
8
102°
82°
9
101°
82°
10
101°
78°
11
96°
76°
12
103°
78°
13
99°
78°
14
99°
77°
15
99°
76°
16
99°
74°
17
99°
72°
18
94°
69°
19
89°
68°
20
86°
64°
21
88°
66°
22
87°
66°
23
88°
65°
24
86°
63°
25
90°
68°
26
89°
69°
27
89°
68°
28
88°
68°
29
89°
67°
30
87°
67°
1
88°
66°
2
87°
66°
3
87°
65°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Sunnyvale
Sunnyvale's September 2026 forecast shows daily high temperatures ranging from 86° to 103°, with overnight lows between 63° and 78°. The average high for September is 92° with an average low of 69°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how September weather will actually feel in Sunnyvale. See also: October | November | December.
