S
M
T
W
T
F
S
30
68°
50°
31
68°
51°
1
67°
53°
2
71°
53°
3
76°
47°
4
76°
53°
5
73°
49°
6
69°
48°
7
74°
52°
8
66°
49°
9
66°
51°
10
67°
52°
11
64°
45°
12
65°
47°
13
65°
48°
14
64°
47°
15
64°
43°
16
63°
45°
17
63°
48°
18
Hist. Avg.
66°
46°
19
Hist. Avg.
66°
46°
20
Hist. Avg.
65°
46°
21
Hist. Avg.
65°
46°
22
Hist. Avg.
65°
45°
23
Hist. Avg.
64°
45°
24
Hist. Avg.
64°
45°
25
Hist. Avg.
64°
45°
26
Hist. Avg.
63°
45°
27
Hist. Avg.
63°
45°
28
Hist. Avg.
63°
45°
29
Hist. Avg.
62°
44°
30
Hist. Avg.
62°
44°
1
Hist. Avg.
62°
44°
2
Hist. Avg.
61°
44°
3
Hist. Avg.
61°
44°
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 63° to 76°, with overnight lows between 43° and 53°. The average high for September is 68° 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.
