The year in numbers
| Month | Open coast | Bay of Kotor | Swimmable? |
|---|---|---|---|
| April | 15–16°C | 14–15°C | No |
| May | 18–19°C | 17–18°C | Brief and brave |
| June | 22–23°C | 21–22°C | Yes |
| July | 24–25°C | 23–25°C | Yes |
| August | 25–26°C | 25–27°C | Yes |
| September | 24–25°C | 24–26°C | Yes, and best |
| October | 21–22°C | 20–22°C | Yes, for most |
| November | 18–19°C | 17–18°C | Brief and brave |
| December – March | 13–15°C | 12–14°C | No |
Why September beats June
Water has enormous thermal mass. It takes the whole summer to warm and most of the winter to cool, so the sea lags the air by about two months. June air is warmer than September air; September water is warmer than June water by two or three degrees.
Two or three degrees is the difference between getting in gradually and walking straight in. It is the single strongest argument for booking the second half of September rather than the middle of June.
The bay is a different sea
The Bay of Kotor is nearly enclosed, deep, and fed by cold karst springs — including submarine ones that push freshwater up from below. The result is a bay that behaves unlike the open coast in both directions.
- In high summer the shallow inner bays around Kotor and Risan can run a degree or two warmer than the open sea, because the water sits still and shallow.
- Near the springs, particularly around Morinj and parts of Risan, you swim through cold layers without warning. It is startling rather than dangerous.
- The water is less salty in the inner bay. People notice they float less well and blame themselves.
Where the water is clearest
The open coast south of Budva — Sveti Stefan, Petrovac, Buljarica — has the clearest water, because it is exposed and there is no river inflow. The inner Bay of Kotor is calmer and more sheltered but murkier after rain, when the mountains dump run-off into it.
Ulcinj's Velika Plaža is sandy rather than pebbled, which means the water clouds when the wind picks up. Beautiful, warm and shallow; never mirror-clear.
What the wind does
The bura, the cold north-easterly off the mountains, flattens the sea and drops the surface temperature by a degree or two overnight. The jugo, warm from the south, builds swell and keeps the warmth. A run of bura days in late September can end the swimming season abruptly, a week earlier than the averages suggest.
