Koper weather in May

In May, Koper sees average daytime highs of 20°C and overnight lows near 14°C, with 103 mm of rain across 11.7 wet days and about 14.7 hours of daylight. It is the 5th-warmest and 5th-wettest month of the year here.

Highs climb over the month, from about 19°C in the first days to 22°C by the end. The sky is clear or mostly clear about 37% of the time in May, and the air most often feels dry.

Daylight stretches from about 14 hours at the start of May to 15 h 12 min by month's end. Set against the rest of the year, May is Koper's 5th-clearest and 9th-windiest month. For the whole year in context, see Koper's year-round climate.

Daytime high
20°
5th warmest
Overnight low
14°
8th coldest
Rainfall
103 mm
11.7 wet days
Daylight
14 h 42 min
4:40 AM – 7:22 PM
Cloud cover
53%
5th clearest
Wind
9 km/h
9th windiest
Solar energy
5.84 kWh/m²
Travel score
6.2
out of 10

Koper is city in southwest Slovenia.

Air quality
Good
PM10 16.8 µg/m³ · 2019
Density
1,981/km²
people per km²

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

Temperature in May

Average highAverage lowShaded bands: 10–90% of days

Highs climb over the month, from about 19°C in the first days to 22°C by the end.

A typical May day in Koper reaches about 20°C in the afternoon and slips back to 14°C overnight — a 6°C spread between the day's warmth and the night's chill. On most days the high lands between 16°C and 24°C. Set against its neighbours, May runs about 5°C warmer than April and about 4°C cooler than June.

10°15°20°25°30°151015202531
Avg high (°C)Avg low (°C)
11812
21812
31912
41912
51913
61913
71913
81913
91913
101913
112013
122013
132013
142014
152014
162014
172014
182014
192114
202114
212114
222115
232115
242115
252115
262215
272215
282215
292216
302216
312216

How May really feels in Koper

Once humidity and wind are folded in, May 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

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

Koper weather by month

How May compares with the rest of the year at a glance. May is the 5th-warmest and 5th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 779.10.98.91.1
Feb / 858.51.510.11.6
Mar12° / 869.30.711.63.3
Apr16° / 9511.20.213.24.8
May20° / 14°10311.7014.76.2
Jun24° / 18°8510.1015.47.0
Jul27° / 20°628.2015.17.2
Aug27° / 20°898.5013.97.1
Sep22° / 16°14710.3012.36.8
Oct18° / 12°15712.2010.75.5
Nov12° / 16712.70.39.33.1
Dec / 1129.90.98.61.5

Cloud cover in May

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 37% of the time in May.

Beyond those clear spells, partly cloudy skies cover about 19% of May, with mostly cloudy or overcast conditions the remaining 44%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
15149
25149
35149
45248
55149
65248
75248
85347
95347
105446
115446
125446
135545
145545
155545
165644
175644
185743
195743
205842
215941
226040
236040
246139
256139
266040
276040
286139
296139
306139
316139

Chance of precipitation in May

Any precipitation

Koper gets around 103 mm of rain over 11.7 wet days in May. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 38% and peaks near 40% on the wettest days.

0%10%20%30%40%50%151015202531
Rain chance (%)
139
239
340
440
540
640
740
840
940
1040
1139
1239
1339
1439
1539
1639
1739
1839
1938
2038
2137
2237
2337
2436
2536
2636
2736
2836
2936
3037
3137

Humidity in May

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, May lands in the dry band about 62% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)
1901000
2881200
3861400
4841600
5821800
6792010
7772210
8752410
9732610
10722710
11702910
12683020
13663220
14653320
15633430
16613540
17603640
18593650
19573760
20563770
21543880
22533890
235238100
245038121
254838131
264638151
274438171
284238191
294038211
303738231
313538252

Wind in May

Winds average 9 km/h in May.

Across May, daily wind ranges from about 8 km/h on the calmest days to 9 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202531
Wind speed (km/h)Feels
19calm
29calm
39calm
49calm
59calm
69calm
79calm
89calm
99calm
109calm
119calm
129calm
139calm
149calm
159calm
169calm
179calm
189calm
199calm
209calm
219calm
229calm
239calm
249calm
259calm
269calm
279calm
289calm
299calm
309calm
318calm

Sunrise & sunset in May

DaylightNight

Daylight runs from about 14 hours at the start of May to 15 h 12 min by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 72 minutes over May. Sunrise moves from 5:01 AM to 4:27 AM, and sunset from 7:03 PM to 7:38 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.05:017:03
214.15:007:05
314.14:587:06
414.24:577:07
514.24:557:09
614.34:547:10
714.34:527:11
814.44:517:12
914.44:497:14
1014.44:487:15
1114.54:477:16
1214.54:457:17
1314.64:447:19
1414.64:437:20
1514.74:427:21
1614.74:407:22
1714.74:397:23
1814.84:387:25
1914.84:377:26
2014.84:367:27
2114.94:357:28
2214.94:347:29
2315.04:337:30
2415.04:327:31
2515.04:317:32
2615.04:307:33
2715.14:307:34
2815.14:297:35
2915.14:287:36
3015.24:277:37
3115.24:277:38

Solar energy in May

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in May, about 5.84 kWh/m².

For context, solar energy here swings from a low near 1.2 kWh/m² to a high of 6.47 kWh/m² in July across the year — May's 5.84 kWh/m² sits near the top of that range.

0246151015202531
Solar energy (kWh/m²)Level
15.4Bright
25.4Bright
35.5Bright
45.5Bright
55.5Bright
65.5Bright
75.6Bright
85.6Bright
95.6Bright
105.6Bright
115.7Bright
125.7Bright
135.7Bright
145.7Bright
155.8Bright
165.8Bright
175.8Bright
185.9Bright
195.9Bright
205.9Bright
216.0Bright
226.0Bright
236.0Intense
246.0Intense
256.1Intense
266.1Intense
276.1Intense
286.2Intense
296.2Intense
306.2Intense
316.2Intense
Planning a trip in May

Is May a good time to visit Koper?

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

6.2
Sightseeing
5th-best month of the year
3.4
Beach & pool
5th-best month of the year

May is a reasonable time to visit Koper for sightseeing.

What to pack for Koper in May

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

In May, Koper sees daytime highs around 20°C and nights near 14°C. Worth packing: rain gear and sun protection. About 12 days see rain.

rain gearsun protection

Sea temperature near Koper in May

The nearest coast averages about 18°C in May — 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 Koper in May

LowModerateHighVery highExtreme

Clear-sky midday UV in May 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 Koper 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 Koper in May

GoodModeratePoorUnhealthyVery unhealthy

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

Air quality in Koper 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 Koper?

Koper sits at 45.5°N, 13.7°E, 12 m above sea level, in Slovenia. The nearest listed city is Trieste, 12 km away.

DivačaMonfalconeGoriziaPostojnaNova Gorica

Topography around Koper

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

Within 3 km, the terrain around Koper has only modest variations in elevation — a maximum elevation change of 238 m around an average of 24 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 575 m; within 80 km, very significant variations in elevation — a maximum elevation change of 2,150 m.

The land around Koper is covered by water (34%) and artificial surfaces (23%) within 3 km, trees (46%) and water (34%) within 16 km, and trees (48%) and water (29%) within 80 km.

3 km
238 m
16 km
575 m
80 km
2,150 m
treesshrubsgrasslandcroplandartificial surfaceswaterwetland
May weather nearby: Trieste 12 km · Piran 13 km · Divača 24 km · Monfalcone 32 km · Gorizia 44 km · Postojna 45 km · Nova Gorica 46 km · Rovinj 52 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 Koper (45.5482°, 13.7296°, elevation 12 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).