Sea Temperature in Mljet Island in September (2026) – Swimming Guide
Sea temperature in Mljet Island in September averages 25.3°C (typical range 23°C–27.4°C). Swimming conditions, 10-day trends, and top beaches.
Typical Range: 23°C – 27.4°C
Standard swimwear. No wetsuit needed; water is warm and welcoming even for infants.
Povoljni termički uvjeti za cjelodnevni boravak uz more
4 rainy days · UV Index 6
Sea Temperature Progression in September by Decade
Multi-year oceanographic measurements across early, mid, and late month:
Annual Oceanographic Climatology for Mljet Island
Multi-year historical records by the Croatian Meteorological and Hydrological Service (DHMZ) & Institute of Oceanography and Fisheries (IZOR)
| Month | Sea Temperature | Day Air | Night Air | Sun Hours | Rain Days | Swimming Verdict |
|---|---|---|---|---|---|---|
| January | 14.2°C (12.6° – 15.7°) | 13.1°C | 6.7°C | 5 h | 8 d | Crisp & cool |
| February | 13.4°C (11.8° – 14.8°) | 13.6°C | 7°C | 5.8 h | 7 d | Crisp & cool |
| March | 14.4°C (12.8° – 16°) | 16.2°C | 9.2°C | 7 h | 7 d | Crisp & cool |
| April | 16.6°C (15° – 18.8°) | 19.8°C | 12.3°C | 8.5 h | 7 d | Crisp & cool |
| May → | 20.2°C (18° – 22.7°) | 24.5°C | 16.6°C | 10 h | 5 d | Refreshing & invigorating |
| June → | 24.3°C (21.7° – 27°) | 28.8°C | 20.4°C | 11.5 h | 4 d | Comfortable & warm |
| July → | 26.6°C (24.7° – 29°) | 31.8°C | 23.2°C | 12.5 h | 2 d | Very warm & ideal |
| August → | 27.6°C (25.6° – 30°) | 31.7°C | 23°C | 11.8 h | 2 d | Very warm & ideal |
| September → | 25.3°C (23° – 27.4°) | 26.8°C | 18.8°C | 9.4 h | 4 d | Very warm & ideal |
| October → | 21.9°C (19.8° – 24.2°) | 21.9°C | 15°C | 7.2 h | 7 d | Comfortable & warm |
| November | 18.2°C (16.2° – 20°) | 17.1°C | 10.7°C | 5.2 h | 9 d | Refreshing & invigorating |
| December | 15.4°C (13.7° – 17°) | 13.7°C | 7.6°C | 4.4 h | 8 d | Crisp & cool |
Top Rated Beaches in Mljet Island for this Season
Curated bathing spots featuring verified water cleanliness and supreme swimming comfort (8 verified locations):
Expert Swimming & Marine Tips
🌬️ Winds & Marine Currents
Summer afternoons regularly welcome the refreshing Maestral (NW) sea breeze. A strong Bura (NE) wind can temporarily drop surface water temperatures by 1–2°C, especially in shallow coastal coves.
☀️ Sun Protection & UV Exposure
In peak summer months, the UV index regularly surpasses 8. Limit unprotected sunbathing between 11:00 AM and 4:00 PM, and always use high-factor water-resistant sunscreen.
🤿 Water Clarity & Sea Urchins
The Adriatic Sea here consistently scores excellent water quality under EU bathing water directives. Sea urchins on rocky shallows serve as nature’s bio-indicator of immaculate water purity.
Frequently Asked Questions – Sea Temperature in Mljet Island
Is it warm enough to swim in Mljet Island in September?
In September, average sea temperature in Mljet Island is 25.3°C. Very warm & ideal / Perfect for long swims & kids. Standard swimwear. No wetsuit needed; water is warm and welcoming even for infants.
What is the air temperature and daily sunshine in September?
Average daytime air temperature reaches 26.8°C (18.8°C at night), featuring approximately 9.4 hours of bright sunshine daily and only 4 rainy days.
How does sea temperature evolve from early to late September?
During early September (1st–10th) water averages 26.2°C, mid-month (11th–20th) sits at 25.3°C, and late month (21st–31st) reaches 24.4°C.