S
M
T
W
T
F
S
30
90°
71°
31
87°
65°
1
91°
67°
2
93°
68°
3
92°
72°
4
91°
65°
5
92°
71°
6
86°
70°
7
96°
73°
8
91°
60°
9
84°
59°
10
83°
60°
11
87°
62°
12
86°
64°
13
89°
59°
14
82°
60°
15
83°
57°
16
84°
55°
17
84°
54°
18
78°
51°
19
81°
57°
20
77°
56°
21
82°
57°
22
82°
58°
23
81°
58°
24
79°
57°
25
70°
57°
26
76°
56°
27
79°
56°
28
77°
55°
29
72°
53°
30
75°
45°
1
63°
43°
2
64°
40°
3
64°
40°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Fullerton
Fullerton's September 2026 forecast shows daily high temperatures ranging from 63° to 96°, with overnight lows between 40° and 73°. The average high for September is 80° with an average low of 57°. 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 Fullerton. See also: October | November | December.
