S
M
T
W
T
F
S
30
65°
53°
31
72°
48°
1
64°
51°
2
66°
53°
3
68°
48°
4
68°
48°
5
71°
50°
6
73°
47°
7
68°
51°
8
72°
49°
9
73°
50°
10
69°
51°
11
65°
51°
12
71°
50°
13
63°
53°
14
66°
52°
15
69°
51°
16
73°
49°
17
73°
50°
18
67°
48°
19
64°
47°
20
67°
46°
21
69°
46°
22
N/A
23
65°
49°
24
62°
52°
25
62°
49°
26
62°
47°
27
64°
50°
28
62°
50°
29
64°
49°
30
63°
48°
1
62°
47°
2
60°
47°
3
60°
49°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in San Juan Island
San Juan Island's September 2026 forecast shows daily high temperatures ranging from 60° to 65°, with overnight lows between 47° and 52°. The average high for September is 62° with an average low of 49°. 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 Juan Island. See also: October | November | December.
