S
M
T
W
T
F
S
30
87°
78°
31
87°
77°
1
88°
78°
2
85°
77°
3
87°
77°
4
87°
76°
5
88°
77°
6
87°
75°
7
88°
76°
8
89°
76°
9
90°
75°
10
89°
75°
11
89°
76°
12
90°
76°
13
90°
75°
14
89°
75°
15
90°
74°
16
89°
75°
17
90°
76°
18
89°
76°
19
90°
75°
20
89°
77°
21
90°
76°
22
89°
75°
23
90°
76°
24
90°
76°
25
89°
75°
26
90°
76°
27
90°
77°
28
89°
76°
29
90°
77°
30
90°
77°
1
89°
76°
2
90°
77°
3
88°
77°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in San Juan
San Juan's September 2026 forecast shows daily high temperatures ranging from 85° to 90°, with overnight lows between 74° and 78°. The average high for September is 89° with an average low of 76°. 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 San Juan. See also: October | November | December.
