S
M
T
W
T
F
S
30
77°
55°
31
64°
56°
1
73°
59°
2
70°
55°
3
77°
57°
4
74°
56°
5
73°
52°
6
76°
56°
7
90°
51°
8
93°
63°
9
98°
69°
10
87°
61°
11
75°
59°
12
73°
53°
13
77°
58°
14
76°
58°
15
74°
59°
16
75°
58°
17
75°
60°
18
75°
59°
19
76°
59°
20
74°
60°
21
77°
57°
22
73°
57°
23
75°
58°
24
77°
57°
25
76°
57°
26
73°
59°
27
79°
60°
28
80°
61°
29
80°
61°
30
79°
60°
1
80°
60°
2
79°
59°
3
80°
60°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Castro Valley
Castro Valley's September 2026 forecast shows daily high temperatures ranging from 73° to 98°, with overnight lows between 53° and 69°. 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 Castro Valley. See also: October | November | December.
