S
M
T
W
T
F
S
30
90°
79°
31
91°
78°
1
90°
77°
2
89°
79°
3
90°
78°
4
90°
78°
5
89°
79°
6
90°
79°
7
90°
78°
8
89°
79°
9
90°
79°
10
90°
78°
11
91°
78°
12
89°
79°
13
90°
78°
14
89°
79°
15
89°
77°
16
90°
78°
17
89°
79°
18
90°
78°
19
90°
77°
20
89°
77°
21
89°
76°
22
88°
75°
23
89°
77°
24
88°
75°
25
86°
75°
26
85°
77°
27
86°
77°
28
86°
76°
29
87°
76°
30
85°
77°
1
86°
75°
2
87°
78°
3
87°
78°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Upper Keys
Upper Keys's September 2026 forecast shows daily high temperatures ranging from 85° to 91°, with overnight lows between 75° and 79°. The average high for September is 89° with an average low of 78°. 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 Upper Keys. See also: October | November | December.
