S
M
T
W
T
F
S
30
91°
81°
31
91°
78°
1
87°
82°
2
89°
83°
3
88°
82°
4
88°
81°
5
86°
80°
6
87°
80°
7
88°
81°
8
90°
82°
9
88°
81°
10
87°
80°
11
89°
82°
12
86°
80°
13
89°
80°
14
88°
81°
15
88°
80°
16
88°
81°
17
90°
81°
18
90°
80°
19
91°
81°
20
90°
81°
21
89°
80°
22
89°
80°
23
88°
78°
24
88°
77°
25
89°
80°
26
90°
80°
27
89°
81°
28
90°
81°
29
88°
80°
30
89°
80°
1
88°
79°
2
88°
80°
3
87°
79°
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 86° to 91°, with overnight lows between 77° and 83°. The average high for September is 88° with an average low of 80°. 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.
