S
M
T
W
T
F
S
30
77°
57°
31
79°
57°
1
78°
49°
2
76°
50°
3
70°
55°
4
74°
56°
5
74°
57°
6
75°
49°
7
75°
48°
8
70°
49°
9
71°
55°
10
69°
55°
11
75°
53°
12
70°
48°
13
67°
51°
14
66°
50°
15
66°
46°
16
67°
45°
17
66°
51°
18
67°
45°
19
65°
49°
20
66°
52°
21
70°
50°
22
69°
43°
23
67°
44°
24
63°
50°
25
64°
45°
26
68°
42°
27
Hist. Avg.
65°
45°
28
Hist. Avg.
64°
45°
29
Hist. Avg.
64°
44°
30
Hist. Avg.
64°
44°
1
Hist. Avg.
63°
44°
2
Hist. Avg.
63°
43°
3
Hist. Avg.
62°
43°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in Southwest Harbor
Southwest Harbor's September 2026 forecast shows daily high temperatures ranging from 63° to 79°, with overnight lows between 42° and 57°. The average high for September is 70° with an average low of 50°. 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 Southwest Harbor. See also: October | November | December.
