S
M
T
W
T
F
S
30
72°
67°
31
73°
65°
1
73°
64°
2
74°
63°
3
72°
61°
4
70°
62°
5
70°
62°
6
71°
63°
7
72°
64°
8
74°
62°
9
72°
62°
10
72°
63°
11
71°
63°
12
72°
65°
13
74°
67°
14
77°
67°
15
78°
66°
16
78°
69°
17
79°
67°
18
79°
67°
19
77°
68°
20
78°
66°
21
77°
65°
22
76°
63°
23
72°
65°
24
74°
64°
25
78°
66°
26
72°
63°
27
70°
65°
28
71°
65°
29
Hist. Avg.
74°
63°
30
Hist. Avg.
74°
62°
1
Hist. Avg.
74°
62°
2
Hist. Avg.
74°
62°
3
Hist. Avg.
74°
62°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in Costa Mesa
Costa Mesa's September 2026 forecast shows daily high temperatures ranging from 70° to 79°, with overnight lows between 61° and 69°. The average high for September is 74° with an average low of 65°. 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.
