S
M
T
W
T
F
S
30
88°
66°
31
91°
66°
1
93°
70°
2
94°
71°
3
94°
72°
4
96°
72°
5
93°
70°
6
82°
62°
7
82°
60°
8
88°
71°
9
88°
68°
10
80°
56°
11
83°
63°
12
82°
61°
13
85°
62°
14
84°
61°
15
76°
54°
16
71°
53°
17
71°
50°
18
72°
51°
19
69°
47°
20
71°
48°
21
76°
51°
22
73°
56°
23
75°
55°
24
79°
56°
25
80°
56°
26
80°
57°
27
79°
57°
28
80°
56°
29
80°
57°
30
79°
56°
1
76°
50°
2
66°
45°
3
65°
42°
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 88°, with overnight lows between 42° and 71°. The average high for September is 77° with an average low of 55°. 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.
