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