S
M
T
W
T
F
S
30
82°
68°
31
81°
67°
1
80°
63°
2
74°
60°
3
73°
61°
4
74°
59°
5
74°
59°
6
76°
65°
7
80°
66°
8
79°
65°
9
75°
65°
10
78°
64°
11
80°
65°
12
80°
65°
13
79°
66°
14
79°
56°
15
72°
55°
16
69°
56°
17
72°
55°
18
70°
54°
19
71°
55°
20
70°
56°
21
76°
57°
22
76°
60°
23
75°
52°
24
76°
52°
25
71°
51°
26
68°
52°
27
72°
58°
28
73°
58°
29
74°
50°
30
70°
50°
1
66°
54°
2
67°
55°
3
71°
55°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Holtsville
Holtsville's September 2026 forecast shows daily high temperatures ranging from 66° to 82°, with overnight lows between 50° and 68°. The average high for September is 74° with an average low of 59°. 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 Holtsville. See also: October | November | December.
