Alpharetta weather in September

In September, Alpharetta sees average daytime highs of 82°F and overnight lows near 64°F, with 3.6 in of rain across 8.7 wet days and about 12.2 hours of daylight. It is the 4th-warmest and 10th-wettest month of the year here.

Highs ease over the month, from about 85°F in the first days to 78°F by the end. The sky is clear or mostly clear about 39% of the time in September, and the air most often feels muggy.

Daylight stretches from about 12 h 42 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Alpharetta's 3rd-clearest and 9th-windiest month. For the whole year in context, see Alpharetta's year-round climate.

Daytime high
82°
4th warmest
Overnight low
64°
9th coldest
Rainfall
3.6 in
8.7 wet days
Daylight
12 h 12 min
6:25 AM – 6:38 PM
Cloud cover
53%
3rd clearest
Wind
6 mph
9th windiest
Solar energy
4.61 kWh/m²
Travel score
6.4
out of 10

Alpharetta is city in north Fulton County, Georgia, United States.

Density
901/km²
people per km²
Founded
1858

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 85°F in the first days to 78°F by the end.

A typical September day in Alpharetta reaches about 82°F in the afternoon and slips back to 64°F overnight — a 18°F spread between the day's warmth and the night's chill. On most days the high lands between 74°F and 89°F. Set against its neighbours, September runs about 5°F cooler than August and about 10°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18568
28568
38568
48567
58467
68467
78467
88466
98466
108366
118365
128365
138365
148365
158264
168264
178264
188164
198163
208163
218063
228062
238062
247962
257961
267961
277860
287860
297860
307759

How September really feels in Alpharetta

Once humidity and wind are folded in, September averages 0 days that feel above 90°F and 0 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Alpharetta weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 10th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan52° / 34°4.610.40.7102.8
Feb56° / 37°4.6100.510.73.7
Mar64° / 44°4.710.30.111.75.6
Apr72° / 51°4.09.6012.86.7
May79° / 60°3.49.8013.76.7
Jun85° / 68°4.113.7014.24.8
Jul88° / 71°4.114.60144.1
Aug87° / 70°4.112.7013.34.5
Sep82° / 64°3.68.7012.26.4
Oct72° / 53°3.47.2011.17.3
Nov62° / 42°3.98.5010.25.6
Dec54° / 37°4.610.30.39.83.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 39% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 17% of September, with mostly cloudy or overcast conditions the remaining 44%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15446
25446
35446
45545
55545
65545
75644
85644
95842
105842
115743
125842
135842
145743
155842
165743
175644
185644
195545
205545
215545
225545
235545
245644
255644
265743
275743
285743
295842
305842

Chance of precipitation in September

Any precipitation

Alpharetta gets around 3.6 in of rain over 8.7 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 29% and peaks near 33% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
133
232
332
431
530
630
729
828
928
1028
1127
1227
1327
1427
1528
1628
1728
1829
1929
2029
2129
2229
2329
2428
2528
2627
2727
2826
2926
3026

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels muggy — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the muggy band about 30% of days. Sticky, muggy-or-worse air turns up on roughly 41% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
139234224
2310234222
3410244121
4411254019
5512264018
6513263916
7614273715
8715283614
9816283513
10917293412
111017293311
121118293210
131218293110
14131929319
15131928309
16141928299
17151929298
18162028288
19172028278
20192028268
21202027267
22222027257
23232026256
24252025246
25272024245
26282124235
27302123224
28312122224
29332122213
30342121203

Wind in September

Winds average 6 mph in September.

Across September, daily wind ranges from about 5 mph on the calmest days to 6 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
15calm
25calm
35calm
45calm
55calm
65calm
75calm
85calm
95calm
105calm
115calm
125calm
135calm
145calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
306calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 42 min at the start of September to 11 h 42 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 60 minutes over September. Sunrise moves from 6:15 AM to 6:35 AM, and sunset from 6:59 PM to 6:17 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.76:156:59
212.76:156:58
312.76:166:56
412.66:176:55
512.66:176:54
612.66:186:52
712.56:196:51
812.56:206:49
912.56:206:48
1012.46:216:46
1112.46:226:45
1212.46:226:44
1312.36:236:42
1412.36:246:41
1512.26:256:39
1612.26:256:38
1712.26:266:36
1812.16:276:35
1912.16:276:33
2012.16:286:32
2112.06:296:30
2212.06:306:29
2312.06:306:28
2411.96:316:26
2511.96:326:25
2611.86:326:23
2711.86:336:22
2811.86:346:20
2911.76:356:19
3011.76:356:17

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.61 kWh/m².

For context, solar energy here swings from a low near 2.29 kWh/m² to a high of 6.05 kWh/m² in May across the year — September's 4.61 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.0Bright
25.0Bright
35.0Bright
45.0Bright
55.0Bright
64.9Bright
74.9Bright
84.9Bright
94.9Bright
104.8Bright
114.8Bright
124.8Bright
134.7Bright
144.7Bright
154.7Bright
164.6Bright
174.6Bright
184.5Bright
194.5Bright
204.5Bright
214.4Bright
224.4Bright
234.3Bright
244.3Bright
254.3Bright
264.3Bright
274.3Bright
284.2Bright
294.2Bright
304.2Bright
Planning a trip in September

Is September a good time to visit Alpharetta?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

6.4
Sightseeing
4th-best month of the year
7.0
Beach & pool
1st-best month of the year

September is a reasonable time to visit Alpharetta for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Alpharetta in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Alpharetta sees daytime highs around 82°F and nights near 64°F. Pack light clothes. Worth having: rain gear and sun protection. About 9 days see rain.

light clothesrain gearsun protection

UV index in Alpharetta in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 7 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Alpharetta peaks around July 10 at about 10 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 at about 3 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 11 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateJul 10UV 10Dec 20UV 3
UV index (midday)Level
Jan3Moderate
Feb5Moderate
Mar6High
Apr7High
May8Very high
Jun10Very high
Jul10Very high
Aug8Very high
Sep7Very high
Oct5High
Nov4Moderate
Dec3Moderate

Air quality in Alpharetta in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Alpharetta is worst in July — around 21 µg/m³ PM2.5 (moderate), about 2.7× the cleanest month (January, 8 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1621 µg/m³Jan 118 µg/m³
PM2.5 (µg/m³)Level
Jan8Good
Feb11Good
Mar13Moderate
Apr12Moderate
May15Moderate
Jun18Moderate
Jul21Moderate
Aug18Moderate
Sep13Moderate
Oct11Good
Nov10Good
Dec8Good
Location & terrain

Where is Alpharetta?

Alpharetta sits at 34.1°N, 84.3°W, 1,138 ft above sea level, in United States. The nearest listed city is Milton, 3.7 mi away.

Topography around Alpharetta

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Alpharetta.

Within 2 miles, the terrain around Alpharetta has only modest variations in elevation — a maximum elevation change of 269 ft around an average of 1,102 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 853 ft; within 50 miles, large variations in elevation — a maximum elevation change of 3,848 ft.

The land around Alpharetta is covered by trees (55%) and artificial surfaces (37%) within 2 miles, trees (71%) within 10 miles, and trees (82%) within 50 miles.

2 miles
269 ft
10 miles
853 ft
50 miles
3,848 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Milton 3.7 mi · Roswell 5.6 mi · Johns Creek 6.2 mi · Peachtree Corners 8.1 mi · Dunwoody 9.3 mi · Duluth 9.9 mi · Norcross 11 mi · Sandy Springs 12 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Alpharetta (34.0754°, -84.2941°, elevation 1,138 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).