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
100°
77°
9
100°
77°
10
99°
76°
11
99°
78°
12
101°
76°
13
99°
76°
14
99°
75°
15
97°
71°
16
93°
70°
17
91°
69°
18
91°
68°
19
90°
66°
20
88°
65°
21
87°
64°
22
92°
71°
23
91°
69°
24
89°
69°
25
82°
68°
26
87°
68°
27
86°
67°
28
88°
68°
29
87°
68°
30
86°
60°
1
78°
56°
2
77°
57°
3
75°
56°
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 75° to 101°, with overnight lows between 56° and 78°. The average high for September is 90° 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.
