Postojna weather in September

In September, Postojna sees average daytime highs of 19°C and overnight lows near 11°C, with 176 mm of rain across 12.1 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 1st-wettest month of the year here.

Highs ease over the month, from about 21°C in the first days to 17°C by the end. The sky is clear or mostly clear about 34% 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 Postojna's 4th-clearest and 9th-windiest month. For the whole year in context, see Postojna's year-round climate.

Daytime high
19°
4th warmest
Overnight low
11°
9th coldest
Rainfall
176 mm
12.1 wet days
Daylight
12 h 18 min
5:48 AM – 6:07 PM
Cloud cover
56%
4th clearest
Wind
8 km/h
9th windiest
Solar energy
3.7 kWh/m²
Travel score
5.8
out of 10

Postojna is city in Slovenia.

Density
288/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 21°C in the first days to 17°C by the end.

A typical September day in Postojna reaches about 19°C in the afternoon and slips back to 11°C overnight — a 9°C spread between the day's warmth and the night's chill. On most days the high lands between 14°C and 24°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)
12213
22213
32112
42112
52112
62112
72112
82012
92012
102011
112011
122011
132011
141911
151911
161911
171910
181910
191910
201810
211810
221810
231810
241810
25189
26179
27179
28179
29179
30179

How September really feels in Postojna

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.

Postojna weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 1st-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / -3°909.95.38.90.0
Feb / -2°106105.310.10.2
Mar / 10611.13.711.62.0
Apr14° / 12213.71.213.33.7
May18° / 10°14214.8014.75.3
Jun22° / 13°13714.4015.56.1
Jul25° / 15°12212.7015.26.8
Aug24° / 15°14512.4013.96.7
Sep19° / 11°17612.1012.35.8
Oct14° / 14812.10.410.74.0
Nov / 17212.62.39.31.5
Dec / -2°12210.34.48.50.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 34% 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 48%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15743
25743
35644
45644
55644
65644
75644
85545
95545
105446
115545
125446
135446
145446
155446
165446
175347
185248
195248
205149
215149
225149
235149
245050
254951
264951
274654
284654
294555
304456

Chance of precipitation in September

Any precipitation

Postojna gets around 176 mm of rain over 12.1 wet days in September, the wettest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 42% and peaks near 43% on the wettest days.

0%10%20%30%40%50%151015202530
Rain chance (%)
143
242
342
442
542
642
742
842
942
1043
1143
1243
1343
1443
1543
1643
1742
1842
1942
2041
2141
2241
2340
2440
2540
2640
2741
2841
2942
3043

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 64% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)
14141171
24341151
34540140
44740130
54939120
65139100
7533890
8533890
9543880
10563770
11573760
12583660
13603550
14613450
15643240
16653140
17672940
18682840
19712630
20722530
21742330
22752230
23772120
24782020
25791920
26801820
27801820
28821710
29821710
30821710

Wind in September

Winds average 8 km/h in September.

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

051015151015202530
Wind speed (km/h)Feels
18calm
28calm
38calm
48calm
58calm
68calm
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 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 5:29 AM to 6:06 AM, and sunset from 6:37 PM to 5:39 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.15:296:37
213.15:306:35
313.05:316:33
413.05:336:31
512.95:346:29
612.95:356:27
712.85:366:25
812.85:386:23
912.75:396:21
1012.65:406:19
1112.65:426:17
1212.55:436:15
1312.55:446:13
1412.45:456:11
1512.45:476:09
1612.35:486:07
1712.35:496:05
1812.25:516:03
1912.25:526:01
2012.15:535:59
2112.05:545:57
2212.05:565:55
2311.95:575:53
2411.95:585:51
2511.86:005:49
2611.86:015:47
2711.76:025:45
2811.76:035:43
2911.66:055:41
3011.56:065:39

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 3.7 kWh/m².

For context, solar energy here swings from a low near 1.07 kWh/m² to a high of 6.11 kWh/m² in July across the year — September's 3.7 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.4Bright
24.4Bright
34.3Bright
44.3Bright
54.2Bright
64.2Bright
74.1Bright
84.1Bright
94.0Bright
104.0Moderate
113.9Moderate
123.9Moderate
133.8Moderate
143.8Moderate
153.7Moderate
163.6Moderate
173.6Moderate
183.5Moderate
193.5Moderate
203.5Moderate
213.4Moderate
223.4Moderate
233.3Moderate
243.3Moderate
253.2Moderate
263.2Moderate
273.1Moderate
283.1Moderate
293.0Moderate
303.0Moderate
Planning a trip in September

Is September a good time to visit Postojna?

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

5.8
Sightseeing
4th-best month of the year
2.6
Beach & pool
4th-best month of the year

September is a reasonable time to visit Postojna for sightseeing.

What to pack for Postojna in September

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

In September, Postojna sees daytime highs around 19°C and nights near 11°C. Worth packing: rain gear. About 12 days see rain.

rain gear

Sea temperature near Postojna in September

The nearest coast averages about 21°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 46 km away) is warmest in August at about 23°C and coldest in February near 10°C.

It's comfortable for a long swim from Jun 10 to Sep 22 — about 3.5 months when the water holds above 20°C.

10°15°20°25°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmcomfortable to swim
Sea temperature (°C)Comfort
Jan10Bracing
Feb10Bracing
Mar10Bracing
Apr12Bracing
May17Cool
Jun21Refreshing
Jul23Refreshing
Aug23Refreshing
Sep21Refreshing
Oct18Cool
Nov15Cool
Dec12Bracing

UV index in Postojna 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 Postojna peaks around July 16 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 10 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 16UV 9Jan 10UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar5Moderate
Apr7Very high
May7High
Jun8Very high
Jul9Very high
Aug8Very high
Sep5High
Oct3Moderate
Nov2Low
Dec1Low

Air quality in Postojna 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 Postojna is worst in January — around 19 µg/m³ PM2.5 (moderate), and holds fairly steady the rest of the year.

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateJan 1918 µg/m³Sep 1512 µg/m³
PM2.5 (µg/m³)Level
Jan19Moderate
Feb17Moderate
Mar18Moderate
Apr18Moderate
May15Moderate
Jun16Moderate
Jul14Moderate
Aug13Moderate
Sep12Good
Oct13Moderate
Nov13Moderate
Dec15Moderate
Location & terrain

Where is Postojna?

Postojna sits at 45.8°N, 14.2°E, 0 m above sea level, in Slovenia. The nearest listed city is Divača, 21 km away.

DivačaTriesteLjubljanaKoperNova GoricaGoriziaKranjRijeka

Topography around Postojna

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

Within 3 km, the terrain around Postojna has significant variations in elevation — a maximum elevation change of 409 m around an average of 606 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 1,054 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,695 m.

The land around Postojna is covered by trees (69%) and grassland (20%) within 3 km, trees (77%) within 16 km, and trees (70%) within 80 km.

3 km
409 m
16 km
1,054 m
80 km
2,695 m
treesgrasslandcroplandartificial surfaceswaterwetland
September weather nearby: Divača 21 km · Trieste 37 km · Ljubljana 38 km · Koper 45 km · Nova Gorica 48 km · Gorizia 50 km · Kranj 53 km · Rijeka 53 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 Postojna (45.7743°, 14.2153°, 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).