S
M
T
W
T
F
S
30
73°
56°
31
76°
58°
1
77°
58°
2
77°
57°
3
73°
58°
4
72°
58°
5
76°
57°
6
78°
58°
7
78°
58°
8
77°
57°
9
78°
55°
10
73°
51°
11
72°
51°
12
73°
52°
13
72°
55°
14
71°
54°
15
74°
53°
16
76°
56°
17
75°
59°
18
78°
59°
19
70°
58°
20
71°
58°
21
77°
57°
22
78°
59°
23
75°
58°
24
76°
58°
25
78°
57°
26
77°
58°
27
77°
57°
28
72°
57°
29
72°
58°
30
73°
59°
1
77°
57°
2
79°
58°
3
78°
57°
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 79°, with overnight lows between 51° and 59°. 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.
