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
N/A
14
65°
50°
15
67°
50°
16
69°
51°
17
70°
49°
18
69°
51°
19
68°
51°
20
67°
52°
21
66°
51°
22
67°
50°
23
65°
51°
24
66°
51°
25
66°
50°
26
65°
51°
27
60°
48°
28
60°
48°
29
60°
49°
30
61°
47°
1
59°
48°
2
59°
47°
3
58°
45°
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 58° to 70°, with overnight lows between 45° and 52°. The average high for September is 64° 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 San Juan Island. See also: October | November | December.
