The Slovenia resorts with the warmest sea water temperature in September are Portoroz, Piran and Strunjan.
Below you can see a list of all popular Slovenia resorts and information about sea water temperature in September for the last two years.
| Resort Name | September 2026 | September 2025 | September 2024 |
|---|---|---|---|
| Portoroz | 81.0°F | 78.2°F | 78.8°F |
| Piran | 81.0°F | 78.2°F | 78.8°F |
| Strunjan | 80.7°F | 78.0°F | 78.6°F |
| Koper | 80.4°F | 78.0°F | 78.3°F |
| Isola | 80.4°F | 77.9°F | 78.5°F |
| Cerkno | 78.4°F | 76.2°F | 77.4°F |
| Bohinjsko Jezero | 78.2°F | 75.9°F | 77.3°F |
| Dolenjske Toplice | 77.7°F | 74.2°F | 74.4°F |
Please see following sea water temperature averages charts for the warmest Slovenia resorts in September.
You can also get the same information for the every other month of the year when the average sea water temperature is greater then 70°F.
Slovenia Resorts:
NAME
F°
| Bled |  |
+46 |
| Bohinjsko Jezero | |
+46 |
| Cerkno | |
+50 |
| Dolenjske Toplice | |
+54 |
| Isola | |
+60 |
| Koper | |
+60 |
| Kranjska Gora | |
+46 |
| Ljubljana | |
+52 |
| Maribor | |
+56 |
| Moravske Toplice | |
+58 |
| Piran | |
+60 |
| Portoroz | |
+60 |
| Rogaska Slatina | |
+54 |
| Smarjeske Toplice | |
+54 |
| Strunjan | |
+60 |
