S
M
T
W
T
F
S
30
85°
61°
31
74°
58°
1
82°
59°
2
87°
61°
3
83°
60°
4
78°
55°
5
86°
56°
6
87°
61°
7
88°
61°
8
88°
57°
9
86°
58°
10
84°
55°
11
82°
56°
12
82°
55°
13
84°
56°
14
82°
48°
15
85°
52°
16
84°
53°
17
84°
53°
18
83°
52°
19
83°
52°
20
82°
51°
21
83°
51°
22
83°
50°
23
82°
50°
24
82°
51°
25
80°
49°
26
76°
48°
27
72°
49°
28
72°
48°
29
71°
47°
30
71°
47°
1
72°
45°
2
71°
46°
3
71°
45°
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 71° to 88°, with overnight lows between 45° and 61°. The average high for September is 81° with an average low of 53°. 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.
