S
M
T
W
T
F
S
30
99°
73°
31
99°
73°
1
100°
73°
2
103°
76°
3
101°
79°
4
93°
76°
5
100°
72°
6
97°
76°
7
100°
73°
8
102°
72°
9
100°
75°
10
100°
75°
11
103°
75°
12
99°
78°
13
100°
76°
14
100°
77°
15
100°
76°
16
99°
75°
17
96°
75°
18
96°
73°
19
93°
70°
20
94°
69°
21
92°
69°
22
93°
68°
23
94°
70°
24
93°
70°
25
88°
66°
26
90°
70°
27
86°
70°
28
86°
70°
29
88°
70°
30
89°
69°
1
89°
69°
2
88°
68°
3
86°
69°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in San Marcos
San Marcos's September 2026 forecast shows daily high temperatures ranging from 86° to 100°, with overnight lows between 66° and 78°. The average high for September is 93° with an average low of 71°. 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.
