S
M
T
W
T
F
S
30
85°
61°
31
86°
61°
1
85°
60°
2
84°
60°
3
84°
61°
4
85°
61°
5
84°
62°
6
84°
63°
7
85°
64°
8
84°
63°
9
83°
65°
10
85°
66°
11
87°
65°
12
88°
65°
13
88°
64°
14
87°
67°
15
89°
67°
16
89°
66°
17
88°
66°
18
89°
65°
19
88°
65°
20
88°
67°
21
87°
67°
22
89°
66°
23
90°
66°
24
88°
64°
25
82°
62°
26
80°
61°
27
81°
63°
28
80°
64°
29
84°
61°
30
81°
60°
1
79°
61°
2
79°
63°
3
86°
63°
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 79° to 90°, with overnight lows between 60° and 67°. The average high for September is 85° with an average low of 64°. 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.
