S
M
T
W
T
F
S
30
96°
72°
31
97°
74°
1
97°
73°
2
95°
72°
3
93°
71°
4
91°
72°
5
91°
72°
6
92°
73°
7
95°
73°
8
95°
72°
9
94°
73°
10
95°
73°
11
94°
72°
12
95°
72°
13
94°
71°
14
94°
69°
15
90°
70°
16
90°
70°
17
92°
71°
18
87°
70°
19
87°
69°
20
90°
70°
21
92°
71°
22
87°
70°
23
89°
64°
24
92°
63°
25
85°
62°
26
84°
62°
27
Hist. Avg.
87°
64°
28
Hist. Avg.
87°
64°
29
Hist. Avg.
86°
63°
30
Hist. Avg.
86°
63°
1
Hist. Avg.
86°
63°
2
Hist. Avg.
86°
62°
3
Hist. Avg.
85°
62°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in San Marcos
San Marcos's September 2026 forecast shows daily high temperatures ranging from 84° to 97°, with overnight lows between 62° and 74°. The average high for September is 92° with an average low of 70°. 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 San Marcos. See also: October | November | December.
