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
81°
60°
12
77°
70°
13
79°
67°
14
78°
58°
15
72°
62°
16
75°
65°
17
79°
65°
18
78°
62°
19
74°
58°
20
71°
57°
21
70°
57°
22
70°
55°
23
69°
58°
24
73°
55°
25
65°
51°
26
65°
52°
27
66°
59°
28
73°
56°
29
65°
53°
30
65°
57°
1
66°
57°
2
65°
54°
3
68°
57°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Islip
Islip's September 2026 forecast shows daily high temperatures ranging from 65° to 81°, with overnight lows between 51° and 70°. The average high for September is 71° 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 Islip. See also: October | November | December.
