S
M
T
W
T
F
S
30
85°
51°
31
88°
53°
1
89°
53°
2
88°
52°
3
84°
53°
4
83°
53°
5
87°
52°
6
89°
54°
7
89°
53°
8
88°
54°
9
88°
50°
10
83°
46°
11
82°
45°
12
83°
45°
13
82°
49°
14
81°
48°
15
84°
47°
16
86°
50°
17
84°
54°
18
87°
54°
19
79°
53°
20
79°
53°
21
86°
52°
22
86°
53°
23
83°
53°
24
84°
52°
25
85°
52°
26
84°
53°
27
85°
51°
28
79°
52°
29
78°
51°
30
79°
52°
1
84°
53°
2
85°
52°
3
84°
51°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Port Costa
Port Costa's September 2026 forecast shows daily high temperatures ranging from 78° to 89°, with overnight lows between 45° and 54°. The average high for September is 84° with an average low of 51°. 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 Port Costa. See also: October | November | December.
