S
M
T
W
T
F
S
30
81°
59°
31
80°
57°
1
79°
57°
2
79°
54°
3
77°
53°
4
75°
55°
5
71°
47°
6
70°
55°
7
70°
56°
8
76°
56°
9
78°
57°
10
68°
50°
11
67°
52°
12
69°
52°
13
72°
57°
14
76°
56°
15
77°
51°
16
68°
47°
17
67°
51°
18
71°
50°
19
67°
48°
20
74°
57°
21
74°
53°
22
Hist. Avg.
69°
51°
23
Hist. Avg.
69°
50°
24
Hist. Avg.
68°
50°
25
Hist. Avg.
68°
50°
26
Hist. Avg.
68°
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 67° to 81°, with overnight lows between 47° and 59°. The average high for September is 73° with an average low of 53°. 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.
