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
80°
58°
15
73°
58°
16
71°
59°
17
75°
57°
18
77°
59°
19
72°
58°
20
72°
57°
21
71°
58°
22
74°
57°
23
75°
59°
24
74°
57°
25
77°
58°
26
80°
60°
27
71°
56°
28
70°
52°
29
71°
54°
30
72°
54°
1
77°
55°
2
71°
54°
3
72°
53°
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 70° to 80°, with overnight lows between 52° and 60°. The average high for September is 74° 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.
