S
M
T
W
T
F
S
30
81°
66°
31
76°
61°
1
74°
61°
2
73°
60°
3
73°
60°
4
74°
61°
5
75°
67°
6
74°
67°
7
77°
66°
8
79°
65°
9
80°
64°
10
75°
65°
11
80°
65°
12
81°
64°
13
78°
65°
14
76°
63°
15
79°
54°
16
73°
54°
17
69°
55°
18
69°
54°
19
70°
58°
20
69°
61°
21
74°
60°
22
68°
60°
23
74°
61°
24
75°
59°
25
74°
60°
26
76°
61°
27
76°
57°
28
75°
49°
29
73°
49°
30
64°
54°
1
63°
50°
2
65°
55°
3
63°
53°
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 63° to 81°, with overnight lows between 49° and 67°. The average high for September is 74° 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 Islip. See also: October | November | December.
