S
M
T
W
T
F
S
26
74°
59°
27
79°
59°
28
73°
58°
29
75°
56°
30
79°
54°
31
84°
56°
1
72°
58°
2
71°
56°
3
76°
53°
4
81°
58°
5
87°
59°
6
88°
59°
7
90°
58°
8
83°
56°
9
78°
57°
10
81°
58°
11
82°
59°
12
76°
58°
13
80°
61°
14
85°
60°
15
80°
57°
16
80°
58°
17
78°
57°
18
79°
56°
19
76°
57°
20
76°
56°
21
73°
58°
22
72°
55°
23
75°
59°
24
71°
52°
25
76°
56°
26
79°
59°
27
79°
60°
28
78°
59°
29
73°
57°
30
70°
51°
31
73°
56°
1
69°
55°
2
69°
52°
3
70°
50°
4
72°
55°
5
68°
51°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
August Weather in Mercer Island
Mercer Island's August 2026 forecast shows daily high temperatures ranging from 68° to 90°, with overnight lows between 50° and 61°. The average high for August is 76° with an average low of 56°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how August weather will actually feel in Mercer Island. See also: September | October | November.
