Trieste weather in September

In September, Trieste sees average daytime highs of 21°C and overnight lows near 15°C, with 170 mm of rain across 11.4 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 23°C in the first days to 19°C by the end. The sky is clear or mostly clear about 42% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 h 06 min at the start of September to 11 h 30 min by month's end. Set against the rest of the year, September is Trieste's 4th-clearest and 7th-windiest month. For the whole year in context, see Trieste's year-round climate.

Daytime high
21°
4th warmest
Overnight low
15°
9th coldest
Rainfall
170 mm
11.4 wet days
Daylight
12 h 18 min
5:50 AM – 6:09 PM
Cloud cover
49%
4th clearest
Wind
10 km/h
7th windiest
Solar energy
3.89 kWh/m²
Travel score
6.4
out of 10
Air quality
Moderate
PM2.5 12 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 23°C in the first days to 19°C by the end.

A typical September day in Trieste reaches about 21°C in the afternoon and slips back to 15°C overnight — a 6°C spread between the day's warmth and the night's chill. On most days the high lands between 17°C and 25°C. Set against its neighbours, September runs about 5°C cooler than August and about 5°C warmer than October.

10°15°20°25°30°151015202530
Avg high (°C)Avg low (°C)
12417
22317
32317
42317
52316
62316
72316
82216
92216
102216
112216
122215
132215
142115
152115
162115
172115
182115
192115
202014
212014
222014
232014
242014
252014
261914
271914
281914
291913
301913

How September really feels in Trieste

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.

Trieste 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 / 909.52.78.90.5
Feb / 978.62.910.11.1
Mar11° / 1019.71.611.62.7
Apr15° / 11012.10.513.34.2
May19° / 13°12213014.75.8
Jun23° / 17°11112.2015.46.7
Jul26° / 19°8710.7015.17.0
Aug26° / 19°11110.3013.97.0
Sep21° / 15°17011.4012.36.4
Oct16° / 11°184130.110.74.8
Nov11° / 19513.21.19.32.5
Dec / 12910.12.18.60.9

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 42% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 18% of September, with mostly cloudy or overcast conditions the remaining 39%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16733
26733
36733
46733
56634
66634
76634
86634
96535
106535
116436
126337
136436
146337
156238
166238
176139
185941
195941
205842
215842
225743
235644
245644
255545
265446
275446
285347
295248
305149

Chance of precipitation in September

Any precipitation

Trieste gets around 170 mm of rain over 11.4 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 39% and peaks near 44% on the wettest days.

0%10%20%30%40%50%151015202530
Rain chance (%)
136
237
337
437
537
637
737
838
938
1038
1139
1239
1339
1439
1539
1640
1740
1840
1940
2040
2140
2240
2340
2441
2541
2641
2742
2843
2943
3044

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 41% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)
126273511
227283410
32829339
42930328
53031317
63132317
73133306
83233295
93334295
103335284
113435284
123535273
133635263
143735253
153934252
164034242
174234232
184433222
194632211
204732201
214931191
225130181
235230171
245430160
255430160
265530150
275630140
285630140
295730130
305730130

Wind in September

Winds average 10 km/h in September.

Across September, daily wind ranges from about 9 km/h on the calmest days to 10 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (km/h)Feels
19calm
29calm
39calm
49calm
59calm
69calm
79calm
89calm
910calm
1010calm
1110calm
1210calm
1310calm
1410calm
1510calm
1610calm
1710calm
1810calm
1910calm
2010calm
2110calm
2210calm
2310calm
2410calm
2510calm
2610calm
2710calm
2810calm
2910calm
3010calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 h 06 min at the start of September to 11 h 30 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 96 minutes over September. Sunrise moves from 5:31 AM to 6:08 AM, and sunset from 6:38 PM to 5:41 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.15:316:38
213.15:326:37
313.05:336:35
413.05:356:33
512.95:366:31
612.95:376:29
712.85:386:27
812.85:406:25
912.75:416:23
1012.65:426:21
1112.65:436:19
1212.55:456:17
1312.55:466:15
1412.45:476:13
1512.45:486:11
1612.35:506:09
1712.35:516:07
1812.25:526:05
1912.25:546:03
2012.15:556:01
2112.05:565:59
2212.05:575:57
2311.95:595:55
2411.96:005:53
2511.86:015:51
2611.86:035:49
2711.76:045:47
2811.76:055:45
2911.66:065:43
3011.56:085:41

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 3.89 kWh/m².

For context, solar energy here swings from a low near 1.14 kWh/m² to a high of 6.28 kWh/m² in July across the year — September's 3.89 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.7Bright
24.6Bright
34.5Bright
44.5Bright
54.5Bright
64.4Bright
74.3Bright
84.3Bright
94.2Bright
104.2Bright
114.1Bright
124.1Bright
134.0Bright
143.9Moderate
153.9Moderate
163.8Moderate
173.8Moderate
183.7Moderate
193.7Moderate
203.6Moderate
213.6Moderate
223.5Moderate
233.5Moderate
243.4Moderate
253.4Moderate
263.3Moderate
273.3Moderate
283.2Moderate
293.1Moderate
303.1Moderate
Planning a trip in September

Is September a good time to visit Trieste?

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
4.0
Beach & pool
4th-best month of the year

September is a reasonable time to visit Trieste for sightseeing.

What to pack for Trieste in September

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

In September, Trieste sees daytime highs around 21°C and nights near 15°C. Worth packing: rain gear. About 11 days see rain.

rain gear

Sea temperature near Trieste in September

The nearest coast averages about 23°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea offshore is warmest in August at about 25°C and coldest in February near 10°C.

It's comfortable for a long swim from May 31 to Oct 9 — about 4.3 months when the water holds above 20°C.

10°20°30°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan11Bracing
Feb10Bracing
Mar10Bracing
Apr13Bracing
May18Cool
Jun23Refreshing
Jul25Warm
Aug25Warm
Sep23Refreshing
Oct19Cool
Nov16Cool
Dec13Bracing

UV index in Trieste 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 Trieste peaks around July 15 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 7 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 15UV 8Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar4Moderate
Apr7High
May7High
Jun8Very high
Jul8Very high
Aug7Very high
Sep5Moderate
Oct3Moderate
Nov2Low
Dec1Low

Air quality in Trieste 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 Trieste is worst in January — around 16 µg/m³ PM2.5 (moderate), about 1.8× the cleanest month (September, 9 µg/m³).

Seasonal pattern from CAMS reanalysis, scaled to Trieste's WHO annual average of 12 µg/m³.

01020JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateJan 1816 µg/m³Sep 149 µg/m³
PM2.5 (µg/m³)Level
Jan16Moderate
Feb14Moderate
Mar14Moderate
Apr13Moderate
May11Good
Jun12Good
Jul12Good
Aug10Good
Sep9Good
Oct10Good
Nov10Good
Dec13Moderate
Location & terrain

Where is Trieste?

Trieste sits at 45.6°N, 13.8°E, 2 m above sea level, in Italy. The nearest listed city is Koper, 12 km away.

Topography around Trieste

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

Within 3 km, the terrain around Trieste has significant variations in elevation — a maximum elevation change of 451 m around an average of 72 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 779 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,524 m.

The land around Trieste is covered by artificial surfaces (41%), trees (31%) and water (27%) within 3 km, trees (50%) and water (32%) within 16 km, and trees (52%) and water (23%) within 80 km.

3 km
451 m
16 km
779 m
80 km
2,524 m
treesshrubsgrasslandcroplandartificial surfaceswater
September weather nearby: Koper 12 km · Divača 16 km · Piran 21 km · Monfalcone 26 km · Gorizia 35 km · Nova Gorica 36 km · Postojna 37 km · Udine 63 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 Trieste (45.6495°, 13.7768°, elevation 2 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. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. 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).