S
M
T
W
T
F
S
30
92°
80°
31
90°
80°
1
91°
79°
2
89°
80°
3
90°
80°
4
91°
79°
5
92°
80°
6
91°
79°
7
92°
80°
8
91°
79°
9
91°
79°
10
90°
78°
11
90°
79°
12
91°
79°
13
91°
80°
14
90°
81°
15
91°
81°
16
91°
79°
17
90°
78°
18
89°
79°
19
89°
79°
20
90°
80°
21
88°
79°
22
89°
79°
23
90°
78°
24
91°
79°
25
89°
78°
26
88°
77°
27
89°
77°
28
90°
76°
29
91°
77°
30
91°
77°
1
Hist. Avg.
88°
76°
2
Hist. Avg.
88°
76°
3
Hist. Avg.
88°
76°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Key Biscayne
Key Biscayne's September 2026 forecast shows daily high temperatures ranging from 88° to 92°, with overnight lows between 76° and 81°. The average high for September is 90° with an average low of 79°. 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 Key Biscayne. See also: October | November | December.
