Piran weather in September

In September, Piran sees average daytime highs of 22°C and overnight lows near 19°C, with 142 mm of rain across 9.6 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 2nd-wettest month of the year here.

Highs ease over the month, from about 24°C in the first days to 20°C by the end. The sky is clear or mostly clear about 50% of the time in September, and the air most often feels humid.

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 Piran's 4th-clearest and 7th-windiest month. For the whole year in context, see Piran's year-round climate.

Daytime high
22°
4th warmest
Overnight low
19°
9th coldest
Rainfall
142 mm
9.6 wet days
Daylight
12 h 18 min
5:51 AM – 6:09 PM
Cloud cover
45%
4th clearest
Wind
14 km/h
7th windiest
Solar energy
4.08 kWh/m²
Travel score
6.9
out of 10

Piran is coastal town of Slovenia.

Density
94/km²
people per km²

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 24°C in the first days to 20°C by the end.

A typical September day in Piran reaches about 22°C in the afternoon and slips back to 19°C overnight — a 3°C spread between the day's warmth and the night's chill. On most days the high lands between 19°C and 25°C. Set against its neighbours, September runs about 4°C cooler than August and about 4°C warmer than October.

10°15°20°25°30°151015202530
Avg high (°C)Avg low (°C)
12421
22421
32421
42421
52421
62321
72321
82320
92320
102320
112320
122320
132220
142220
152219
162219
172219
182219
192219
202119
212119
222118
232118
242118
252118
262118
272018
282018
292018
302018

Piran weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 2nd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 839.90.18.91.7
Feb / 858.90.610.11.7
Mar11° / 758.40.311.62.8
Apr14° / 12°759.3013.24.3
May19° / 16°829.3014.76.3
Jun23° / 21°647.3015.47.6
Jul26° / 23°475.6015.17.9
Aug26° / 23°787013.97.7
Sep22° / 19°1429.6012.36.9
Oct18° / 16°14112.3010.75.7
Nov14° / 12°17013.90.19.33.6
Dec10° / 11611.30.48.62.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 50% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 14% of September, with mostly cloudy or overcast conditions the remaining 36%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16931
26832
36832
46832
56832
66832
76733
86832
96733
106733
116634
126535
136634
146535
156436
166337
176337
186238
196238
206238
216139
226139
236139
246040
256139
266040
276040
286040
295941
305941

Chance of precipitation in September

Any precipitation

Piran gets around 142 mm of rain over 9.6 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 33% and peaks near 39% on the wettest days. The odds climb toward the end of the month.

0%10%20%30%40%50%151015202530
Rain chance (%)
128
228
328
429
529
629
730
830
931
1031
1132
1233
1333
1434
1534
1635
1735
1835
1935
2036
2136
2235
2335
2435
2536
2636
2737
2837
2938
3039

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the humid band about 30% of days. Sticky, muggy-or-worse air turns up on roughly 19% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
11419292810
2152029279
3152129278
4162129267
5172130256
6182230256
7192230245
8202230244
9212230234
10222131223
11232131223
12242131213
13252131202
14272131192
15282131192
16292131181
17302130171
18322230151
19332230141
20342330131
21352329120
22362330110
2337243090
2437243080
2538253070
2638253160
2739253150
2839253150
2939253140
3040253140

Wind in September

Winds average 14 km/h in September.

Across September, daily wind ranges from about 13 km/h on the calmest days to 14 km/h at its breeziest. It stays fairly steady from day to day.

05101520151015202530
Wind speed (km/h)Feels
113light breeze
213light breeze
313light breeze
413light breeze
513light breeze
613light breeze
714light breeze
814light breeze
914light breeze
1014light breeze
1114light breeze
1214light breeze
1314light breeze
1414light breeze
1514light breeze
1614light breeze
1714light breeze
1814light breeze
1914light breeze
2014light breeze
2114light breeze
2214light breeze
2314light breeze
2414light breeze
2514light breeze
2614light breeze
2714light breeze
2814light breeze
2914light breeze
3014light breeze

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 5:32 AM to 6:09 AM, and sunset from 6:39 PM to 5:41 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.15:326:39
213.15:336:37
313.05:346:35
413.05:356:33
512.95:376:31
612.95:386:29
712.85:396:27
812.75:406:25
912.75:426:24
1012.65:436:22
1112.65:446:20
1212.55:466:18
1312.55:476:16
1412.45:486:14
1512.45:496:11
1612.35:516:09
1712.35:526:07
1812.25:536:05
1912.25:546:03
2012.15:566:01
2112.05:575:59
2212.05:585:57
2311.96:005:55
2411.96:015:53
2511.86:025:51
2611.86:035:49
2711.76:055:47
2811.76:065:45
2911.66:075:43
3011.56:095:41

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.08 kWh/m².

For context, solar energy here swings from a low near 1.2 kWh/m² to a high of 6.52 kWh/m² in July across the year — September's 4.08 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.8Bright
24.8Bright
34.7Bright
44.7Bright
54.6Bright
64.6Bright
74.5Bright
84.5Bright
94.4Bright
104.3Bright
114.3Bright
124.2Bright
134.2Bright
144.1Bright
154.1Bright
164.0Bright
174.0Moderate
183.9Moderate
193.9Moderate
203.8Moderate
213.8Moderate
223.7Moderate
233.7Moderate
243.6Moderate
253.6Moderate
263.5Moderate
273.5Moderate
283.4Moderate
293.4Moderate
303.3Moderate
Planning a trip in September

Is September a good time to visit Piran?

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

6.9
Sightseeing
4th-best month of the year
4.8
Beach & pool
4th-best month of the year

September is a reasonable time to visit Piran for sightseeing.

What to pack for Piran in September

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

In September, Piran sees daytime highs around 22°C and nights near 19°C. Worth packing: light clothes and rain gear. About 10 days see rain.

light clothesrain gear

Sea temperature near Piran 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 Piran 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 Piran 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 Piran 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 Piran is worst in January — around 22 µg/m³ PM2.5 (moderate), about 1.8× the cleanest month (September, 12 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateJan 1822 µg/m³Sep 1412 µg/m³
PM2.5 (µg/m³)Level
Jan22Moderate
Feb20Moderate
Mar20Moderate
Apr19Moderate
May16Moderate
Jun16Moderate
Jul16Moderate
Aug13Moderate
Sep12Moderate
Oct14Moderate
Nov14Moderate
Dec18Moderate
Location & terrain

Where is Piran?

Piran sits at 45.5°N, 13.6°E, 0 m above sea level, in Slovenia. The nearest listed city is Koper, 13 km away.

TriesteMonfalconeDivačaGoriziaNova GoricaPostojna

Topography around Piran

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

Within 3 km, the terrain around Piran has only modest variations in elevation — a maximum elevation change of 172 m around an average of 10 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 412 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,859 m.

The land around Piran is covered by water (82%) within 3 km, water (65%) and trees (20%) within 16 km, and trees (43%) and water (31%) within 80 km.

3 km
172 m
16 km
412 m
80 km
1,859 m
treesshrubsgrasslandcroplandartificial surfaceswater
September weather nearby: Koper 13 km · Trieste 21 km · Monfalcone 31 km · Divača 36 km · Gorizia 46 km · Nova Gorica 48 km · Rovinj 50 km · Postojna 57 km

Slovenia travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type C / F
230 V · 50 Hz
Prices
≈ 63% of US
price level, 2025
GDP per capita
$37,376
2025
Happiness
6.9 / 10
World Happiness, 2025
Safe drinking water
100%
of population, 2024
Homicide rate
0.6
per 100k, 2023
Road deaths
5.1
per 100k/yr, 2019
Income group
High
World Bank
Religion
Catholic 69%atheist 14%Orthodox 4%non-believer/agnostic 4%

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 Piran (45.5278°, 13.5706°, elevation 0 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).