S
M
T
W
T
F
S
30
77°
61°
31
79°
61°
1
77°
59°
2
77°
60°
3
80°
59°
4
76°
61°
5
75°
61°
6
75°
57°
7
80°
61°
8
80°
61°
9
81°
62°
10
81°
62°
11
80°
61°
12
80°
61°
13
76°
60°
14
74°
59°
15
75°
57°
16
78°
61°
17
80°
62°
18
82°
61°
19
81°
60°
20
81°
61°
21
80°
61°
22
81°
60°
23
79°
60°
24
77°
58°
25
80°
60°
26
80°
61°
27
80°
60°
28
80°
59°
29
78°
55°
30
80°
59°
1
77°
56°
2
72°
52°
3
72°
51°
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 72° to 82°, with overnight lows between 51° and 62°. The average high for September is 78° with an average low of 59°. 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.
