S
M
T
W
T
F
S
30
80°
59°
31
82°
62°
1
85°
62°
2
85°
61°
3
86°
56°
4
84°
53°
5
78°
54°
6
78°
59°
7
79°
58°
8
82°
59°
9
83°
60°
10
78°
59°
11
82°
58°
12
82°
59°
13
81°
59°
14
81°
58°
15
83°
59°
16
83°
57°
17
81°
58°
18
80°
52°
19
80°
50°
20
75°
48°
21
73°
47°
22
72°
55°
23
73°
51°
24
78°
48°
25
71°
47°
26
71°
48°
27
72°
47°
28
76°
52°
29
75°
51°
30
76°
51°
1
71°
52°
2
69°
45°
3
68°
50°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Allentown
Allentown's September 2026 forecast shows daily high temperatures ranging from 68° to 86°, with overnight lows between 45° and 62°. The average high for September is 78° with an average low of 54°. 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 Allentown. See also: October | November | December.
