S
M
T
W
T
F
S
30
89°
71°
31
94°
74°
1
98°
74°
2
97°
75°
3
96°
77°
4
96°
75°
5
98°
74°
6
87°
71°
7
84°
65°
8
95°
74°
9
85°
67°
10
83°
59°
11
84°
68°
12
85°
66°
13
86°
68°
14
86°
61°
15
77°
57°
16
76°
55°
17
78°
59°
18
77°
57°
19
75°
55°
20
77°
54°
21
81°
60°
22
79°
59°
23
80°
59°
24
81°
60°
25
81°
61°
26
80°
60°
27
81°
60°
28
79°
59°
29
80°
60°
30
77°
57°
1
76°
52°
2
66°
48°
3
65°
44°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Monticello
Monticello's September 2026 forecast shows daily high temperatures ranging from 65° to 95°, with overnight lows between 44° and 74°. The average high for September is 80° 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 Monticello. See also: October | November | December.
