S
M
T
W
T
F
S
30
75°
55°
31
66°
54°
1
72°
61°
2
71°
60°
3
73°
58°
4
72°
56°
5
72°
55°
6
74°
58°
7
85°
54°
8
85°
58°
9
85°
64°
10
87°
70°
11
74°
59°
12
72°
58°
13
70°
59°
14
78°
54°
15
77°
56°
16
66°
57°
17
72°
62°
18
70°
58°
19
75°
58°
20
69°
58°
21
71°
58°
22
73°
55°
23
79°
56°
24
79°
58°
25
77°
60°
26
74°
59°
27
73°
59°
28
75°
58°
29
74°
58°
30
75°
57°
1
77°
60°
2
74°
54°
3
77°
54°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in San Mateo
San Mateo's September 2026 forecast shows daily high temperatures ranging from 69° to 79°, with overnight lows between 54° and 60°. The average high for September is 75° with an average low of 57°. 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 Mateo. See also: October | November | December.
