S
M
T
W
T
F
S
30
82°
71°
31
78°
68°
1
74°
64°
2
77°
65°
3
79°
64°
4
78°
64°
5
82°
70°
6
81°
70°
7
77°
70°
8
77°
69°
9
78°
68°
10
77°
67°
11
75°
67°
12
71°
65°
13
72°
67°
14
72°
67°
15
74°
64°
16
77°
68°
17
78°
67°
18
71°
62°
19
71°
63°
20
75°
65°
21
77°
67°
22
75°
67°
23
74°
66°
24
73°
64°
25
74°
66°
26
77°
67°
27
77°
68°
28
76°
67°
29
77°
67°
30
76°
66°
1
77°
67°
2
76°
66°
3
75°
64°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Costa Mesa
Costa Mesa's September 2026 forecast shows daily high temperatures ranging from 71° to 82°, with overnight lows between 62° and 70°. The average high for September is 76° with an average low of 66°. 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 Costa Mesa. See also: October | November | December.
