S
M
T
W
T
F
S
30
79°
62°
31
77°
68°
1
78°
66°
2
75°
65°
3
85°
70°
4
84°
70°
5
80°
66°
6
73°
60°
7
79°
56°
8
80°
61°
9
79°
62°
10
86°
70°
11
78°
62°
12
76°
57°
13
79°
68°
14
73°
59°
15
71°
52°
16
76°
55°
17
80°
66°
18
80°
67°
19
69°
62°
20
69°
60°
21
70°
59°
22
69°
56°
23
69°
54°
24
67°
54°
25
67°
56°
26
62°
57°
27
67°
58°
28
65°
56°
29
71°
57°
30
72°
60°
1
76°
61°
2
74°
61°
3
70°
59°
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 62° to 76°, with overnight lows between 56° and 61°. The average high for September is 69° with an average low of 58°. 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.
