S
M
T
W
T
F
S
30
89°
63°
31
83°
61°
1
82°
67°
2
82°
65°
3
85°
62°
4
86°
68°
5
88°
68°
6
89°
61°
7
86°
61°
8
80°
60°
9
80°
60°
10
82°
63°
11
85°
60°
12
83°
60°
13
78°
59°
14
77°
65°
15
82°
64°
16
84°
57°
17
84°
56°
18
75°
55°
19
74°
56°
20
75°
62°
21
74°
61°
22
75°
55°
23
73°
58°
24
73°
57°
25
75°
60°
26
76°
61°
27
79°
55°
28
79°
52°
29
72°
58°
30
72°
58°
1
71°
59°
2
74°
57°
3
76°
51°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in National Harbor
National Harbor's September 2026 forecast shows daily high temperatures ranging from 71° to 89°, with overnight lows between 51° and 68°. The average high for September is 79° with an average low of 60°. 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 National Harbor. See also: October | November | December.
