Siena weather in September

In September, Siena sees average daytime highs of 25°C and overnight lows near 14°C, with 92 mm of rain across 9 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 3rd-wettest month of the year here.

Highs ease over the month, from about 27°C in the first days to 22°C by the end. The sky is clear or mostly clear about 49% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Siena's 4th-clearest and 9th-windiest month. For the whole year in context, see Siena's year-round climate.

Daytime high
25°
4th warmest
Overnight low
14°
9th coldest
Rainfall
92 mm
9 wet days
Daylight
12 h 18 min
6:00 AM – 6:18 PM
Cloud cover
44%
4th clearest
Wind
8 km/h
9th windiest
Solar energy
4.39 kWh/m²
Travel score
7.1
out of 10
Air quality
Good
PM10 18.4 µg/m³ · 2019

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 27°C in the first days to 22°C by the end.

A typical September day in Siena reaches about 25°C in the afternoon and slips back to 14°C overnight — a 10°C spread between the day's warmth and the night's chill. On most days the high lands between 20°C and 28°C. Set against its neighbours, September runs about 5°C cooler than August and about 5°C warmer than October.

10°20°30°151015202530
Avg high (°C)Avg low (°C)
12716
22716
32716
42716
52615
62615
72615
82615
92615
102615
112515
122515
132514
142514
152514
162414
172414
182414
192414
202414
212313
222313
232313
242313
252313
262313
272213
282213
292212
302212

How September really feels in Siena

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

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
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.

Siena weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 3rd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 558.10.89.21.9
Feb10° / 658.41.210.22.5
Mar14° / 6690.511.64.2
Apr17° / 7911.3013.25.4
May22° / 11°7110.1014.56.7
Jun26° / 15°507.5015.17.4
Jul29° / 17°315014.96.5
Aug29° / 18°406.2013.86.3
Sep25° / 14°929012.37.1
Oct19° / 10°10910.4010.86.2
Nov14° / 12011.60.19.53.8
Dec10° / 79100.58.82.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 49% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 19% of September, with mostly cloudy or overcast conditions the remaining 32%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
18020
27921
37822
47822
57723
67624
77525
87426
97327
107228
117030
127030
136832
146733
156634
166535
176436
186436
196238
206238
216238
226238
236139
246139
256139
266139
276139
286040
296040
306040

Chance of precipitation in September

Any precipitation

Siena gets around 92 mm of rain over 9 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 31% and peaks near 35% on the wettest days. The odds climb toward the end of the month.

0%10%20%30%40%50%151015202530
Rain chance (%)
125
225
326
426
526
627
727
828
929
1029
1130
1230
1331
1431
1532
1632
1733
1833
1933
2034
2134
2234
2334
2434
2534
2634
2734
2834
2935
3035

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the dry band about 36% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)
122323610
22333359
32433348
42634337
52734327
62835326
72835315
82936315
92936305
102936304
113036304
123036294
133136294
143235294
153335284
163434274
173534274
183733264
193833254
204032244
214132234
224332223
234432213
244531203
254631203
264731192
274832182
284932172
295032162
305132161

Wind in September

Winds average 8 km/h in September.

Across September, daily wind ranges from about 7 km/h on the calmest days to 8 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
17calm
27calm
37calm
47calm
57calm
67calm
78calm
88calm
98calm
108calm
118calm
128calm
138calm
148calm
158calm
168calm
178calm
188calm
198calm
208calm
218calm
228calm
238calm
248calm
258calm
268calm
278calm
288calm
298calm
308calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 84 minutes over September. Sunrise moves from 5:43 AM to 6:17 AM, and sunset from 6:46 PM to 5:51 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:436:46
213.05:446:44
312.95:456:42
412.95:476:40
512.85:486:38
612.85:496:36
712.75:506:35
812.75:516:33
912.65:526:31
1012.65:536:29
1112.55:556:27
1212.55:566:25
1312.45:576:23
1412.45:586:22
1512.35:596:20
1612.36:006:18
1712.26:016:16
1812.26:036:14
1912.16:046:12
2012.16:056:10
2112.06:066:08
2212.06:076:06
2311.96:086:05
2411.96:096:03
2511.86:116:01
2611.86:125:59
2711.76:135:57
2811.76:145:55
2911.66:155:53
3011.66:175:51

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.39 kWh/m².

For context, solar energy here swings from a low near 1.43 kWh/m² to a high of 6.97 kWh/m² in July across the year — September's 4.39 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.2Bright
25.2Bright
35.1Bright
45.1Bright
55.0Bright
64.9Bright
74.9Bright
84.8Bright
94.7Bright
104.7Bright
114.6Bright
124.5Bright
134.5Bright
144.4Bright
154.4Bright
164.3Bright
174.3Bright
184.2Bright
194.2Bright
204.1Bright
214.0Bright
224.0Bright
234.0Moderate
243.9Moderate
253.9Moderate
263.8Moderate
273.7Moderate
283.7Moderate
293.6Moderate
303.6Moderate
Planning a trip in September

Is September a good time to visit Siena?

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

7.1
Sightseeing
2nd-best month of the year
6.1
Beach & pool
4th-best month of the year

September is one of the better times to visit Siena for general sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Siena in September

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

In September, Siena sees daytime highs around 25°C and nights near 14°C. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Siena in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 5 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Siena peaks around July 14 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 23 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 14UV 9Dec 23UV 1
UV index (midday)Level
Jan1Low
Feb3Moderate
Mar5Moderate
Apr6High
May6High
Jun8Very high
Jul9Very high
Aug7Very high
Sep5High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Siena 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 Siena is worst in March — around 17 µg/m³ PM2.5 (moderate), and holds fairly steady the rest of the year.

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

01020JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateMar 2016 µg/m³Nov 1712 µg/m³
PM2.5 (µg/m³)Level
Jan14Moderate
Feb14Moderate
Mar17Moderate
Apr16Moderate
May15Moderate
Jun14Moderate
Jul12Good
Aug13Moderate
Sep12Moderate
Oct13Moderate
Nov12Good
Dec12Moderate
Location & terrain

Where is Siena?

Siena sits at 43.3°N, 11.3°E, 322 m above sea level, in Italy. The nearest listed city is Colle di Val d'Elsa, 20 km away.

Topography around Siena

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Siena.

Within 3 km, the terrain around Siena has only modest variations in elevation — a maximum elevation change of 199 m around an average of 283 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 520 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,724 m.

The land around Siena is covered by trees (57%) and grassland (22%) within 3 km, trees (55%) and cropland (24%) within 16 km, and trees (62%) within 80 km.

3 km
199 m
16 km
520 m
80 km
1,724 m
treesshrubsgrasslandcroplandartificial surfaceswater
September weather nearby: Colle di Val d'Elsa 20 km · Poggibonsi 22 km · Montevarchi 30 km · San Giovanni Valdarno 32 km · Arezzo 47 km · Scandicci 50 km · Campo di Marte 51 km · Florence 52 km

Italy travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type C / F / L
230 V · 50 Hz
Prices
≈ 69% of US
price level, 2025
GDP per capita
$43,309
2025
Happiness
6.6 / 10
World Happiness, 2025
Safe drinking water
97%
of population, 2024
Homicide rate
0.6
per 100k, 2023
Road deaths
5.3
per 100k/yr, 2019
Income group
High
World Bank
English
Moderate
EF EPI 513
Religion
Christian 81%unaffiliated 13%Muslim 5%other 1%

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 Siena (43.3182°, 11.3306°, elevation 322 m), 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).