Sea temperature in Croatia lags the air by about two months. Dubrovnik’s water is 21.1 °C in June and 21.8 °C in September; the air is warmer in June, the sea in September. DHMZ publishes sea readings for Split, Hvar and Dubrovnik only. Rates are the booking engine’s job.
The search term does not name a town, so this page does not guess one
Some property searches carry a town in them and some do not. This one does not, and rather than invent a location we have written the page around the question that brings people to a named coastal property in the first place: when is the water warm enough to be the reason for the trip.
There is a hard limit on how well that can be answered anywhere in Croatia, and it is worth stating before the numbers. The DHMZ climate normals for 1971–2000 publish a sea temperature row for three stations: Split, Hvar and Dubrovnik. Zadar, Rovinj, Rijeka and Mali Lošinj carry no sea row at all. Any monthly sea figure you have read for those places has been borrowed from somewhere else, and we will not do that here.
Air and sea do not peak in the same month
Water has an enormous thermal mass and the Adriatic behaves accordingly: it warms late and cools late. The consequence is that for two months of the year the sea is warmer than the air above it in the middle of the day, and those two months are September and October — exactly the ones people cross off.
| Month | Mean air °C | Sea °C | Which is warmer |
|---|---|---|---|
| January | 9.2 | 13.2 | Sea |
| February | 9.4 | 12.8 | Sea |
| March | 11.1 | 13.1 | Sea |
| April | 13.8 | 14.5 | Sea |
| May | 18.3 | 17.2 | Air |
| June | 22.0 | 21.1 | Air |
| July | 24.6 | 22.9 | Air |
| August | 24.8 | 23.3 | Air |
| September | 21.4 | 21.8 | Sea |
| October | 17.6 | 19.5 | Sea |
| November | 13.3 | 16.6 | Sea |
| December | 10.3 | 14.7 | Sea |
Read the last column. The air wins in May, June, July and August and the sea wins in the other eight months. September, the month everyone treats as the end of the season, is the first month of the year in which the water is the warmest thing outside.
Dubrovnik monthly sea temperature, °C. The peak is 23.3 °C in August; September at 21.8 °C is warmer than June at 21.1 °C. Source: DHMZ (meteo.hr), climate normals 1971–2000.
Hvar holds it even later. Its water is 22.4 °C in September and 20.6 °C in October, the highest late-season readings of the three published stations, and 18.0 °C as far out as November. Split sits between the two, at 21.7 °C in September and 19.3 °C in October.
Booking June for the swimming
June has the reputation of being the safe early-summer month, and on air temperature it is: 22.0 °C mean in Dubrovnik and only 44.0 mm of rain. On the water it is the weaker half of a pair. June gives 21.1 °C; September gives 21.8 °C.
If the trip is built around swimming rather than around sitting in the sun, September is the same month with warmer water, fewer people and 86.1 mm of rain against June’s 44.0 mm. The trade is four rain days for warmer sea and a quieter town, and for a lot of people that is a straightforward yes.
One dated snapshot, and why it is not a season
On 6 August 2026 DHMZ read sixteen stations along the coast. The coast-wide mean was 27.5 °C, ranging from 26.0 °C at Split and Šibenik to 29.7 °C in Mljet’s Malo jezero. Those are far above the August normal of 23.3 °C at Dubrovnik, because a single warm day in a single warm summer is not a climate normal.
Quote the snapshot and you will be disappointed; quote the normals and you will be roughly right most years. The difference between the two is the difference between what the sea was doing on one afternoon and what it usually does in that month, and only the second is any use for a booking made months ahead.
Common questions
Which month has the warmest sea in Croatia?
August, at every station where it is published: 23.6 °C at Split, 23.5 °C at Hvar and 23.3 °C at Dubrovnik on the 1971–2000 normals.
Is September warmer than June for swimming?
Yes, at all three published stations. Dubrovnik is 21.8 °C in September against 21.1 °C in June, Hvar 22.4 °C against 20.8 °C, Split 21.7 °C against 21.1 °C.
What is the sea temperature in Rovinj or Zadar?
The 1971–2000 normals do not publish one. Only Split, Hvar and Dubrovnik carry a sea row, and filling the gap from a neighbouring station would be a guess dressed as a figure.
Can you still swim in October?
The water is 19.5 °C at Dubrovnik and 20.6 °C at Hvar, so physically yes. The constraint is the air and the rain: Dubrovnik records 1.9 days at or above 25 °C in October and 120.1 mm of rain.
One thing this page deliberately does not do. It carries no room rate, no star rating, no photograph and no description of the property, because we hold none of that and the register we do hold says nothing about buildings. Rates, availability and what the rooms are like are the booking engine’s job and it does that job well. What no booking engine tells you is which boats exist on the dates you are about to confirm, and that is the whole of this page.
Also on Hotels.com
What do you need to work out next?
Water settled. These come next.
Where to stay
Which kind of stay suits a swimming trip?
Croatian stock is overwhelmingly private apartments, not hotels.
Getting around
What is the shore actually like?
Croatian swimming is pebble and rock, not sand.
When to go
Which week should I choose?
September water beats June water at all three published stations.
Planning
Where is the water warmest?
On 6 August 2026 the range ran 26.0°C to 29.7°C across sixteen stations.
Climate data: DHMZ (meteo.hr), climate normals 1971–2000.