S
M
T
W
T
F
S
30
90°
80°
31
91°
78°
1
90°
79°
2
89°
77°
3
89°
78°
4
88°
77°
5
88°
78°
6
89°
78°
7
88°
75°
8
88°
78°
9
89°
78°
10
88°
77°
11
90°
79°
12
89°
79°
13
88°
78°
14
88°
79°
15
89°
80°
16
89°
78°
17
90°
78°
18
89°
77°
19
88°
78°
20
89°
79°
21
90°
78°
22
88°
77°
23
89°
78°
24
89°
77°
25
87°
77°
26
87°
76°
27
88°
78°
28
88°
76°
29
87°
76°
30
87°
78°
1
88°
79°
2
88°
76°
3
87°
74°
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 87° to 91°, with overnight lows between 74° and 80°. 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.
