S
M
T
W
T
F
S
30
72°
52°
31
80°
49°
1
73°
49°
2
72°
50°
3
71°
56°
4
75°
55°
5
79°
54°
6
79°
56°
7
70°
49°
8
68°
48°
9
69°
48°
10
70°
52°
11
76°
55°
12
74°
55°
13
68°
56°
14
68°
57°
15
67°
55°
16
67°
54°
17
68°
52°
18
66°
52°
19
65°
48°
20
66°
46°
21
67°
45°
22
65°
46°
23
65°
46°
24
68°
50°
25
72°
53°
26
69°
50°
27
Hist. Avg.
67°
49°
28
Hist. Avg.
67°
49°
29
Hist. Avg.
66°
49°
30
Hist. Avg.
66°
49°
1
Hist. Avg.
66°
48°
2
Hist. Avg.
65°
48°
3
Hist. Avg.
65°
48°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in Issaquah
Issaquah's September 2026 forecast shows daily high temperatures ranging from 65° to 80°, with overnight lows between 45° and 57°. The average high for September is 70° with an average low of 51°. 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 Issaquah. See also: October | November | December.
