S
M
T
W
T
F
S
30
74°
55°
31
74°
53°
1
69°
52°
2
66°
53°
3
69°
54°
4
73°
55°
5
72°
53°
6
72°
53°
7
71°
52°
8
71°
52°
9
70°
51°
10
70°
52°
11
69°
51°
12
64°
49°
13
59°
48°
14
57°
45°
15
61°
42°
16
62°
46°
17
64°
39°
18
68°
48°
19
67°
47°
20
70°
49°
21
67°
47°
22
68°
44°
23
65°
45°
24
66°
45°
25
66°
44°
26
64°
34°
27
64°
34°
28
54°
33°
29
57°
36°
30
54°
33°
1
55°
31°
2
52°
32°
3
48°
35°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Thunder Bay
Thunder Bay's September 2026 forecast shows daily high temperatures ranging from 48° to 74°, with overnight lows between 31° and 55°. The average high for September is 65° with an average low of 45°. 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 Thunder Bay. See also: October | November | December.
