September’s sea at Split is 21.7°C, warmer than June’s 21.1°C, and Hvar’s is 22.4°C. On the Split Marjan record for 1948 to 2024 September carries 17 days above 25°C and October carries one. The Croatian season does not fade out gradually; it stops.
September has the warmest water of any month you would call shoulder season
The comparison everybody makes is September against August. The more useful one is September against June, because June is the month people book when they want summer without the peak. At every station with a published sea temperature, September’s water is warmer than June’s, and by a wide margin.
| Station | June sea °C | September sea °C | June days ≥25°C | September days ≥25°C |
|---|---|---|---|---|
| Split (Marjan) | 21.1 | 21.7 | 22.0 | 15.4 |
| Hvar town | 20.8 | 22.4 | 21.5 | 20.7 |
| Dubrovnik | 21.1 | 21.8 | 17.3 | 16.7 |
Hvar gains a degree and a half of water between June and September. Dubrovnik gains seven-tenths and holds 10.3 hours of sun a day, all but identical to August’s 10.5. The land signal is weaker in September and the water signal is stronger, which is exactly the trade a shoulder-season traveller is trying to make.
September · Split (Marjan)
Move it one step to October and the warm-day figure collapses while the sea barely moves. That single step is the most important thing on this page.
The cliff
The Split Marjan station has a record running from 1948 to 2024, a longer and separate dataset from the 1971–2000 normals used elsewhere on this page. On that long record September averages 17 days with a maximum above 25°C. October averages one. There is no gentle taper between them; the warm-day count falls by 94 per cent in four weeks.
Days with a maximum above 25°C at Split Marjan, by month. Source: DHMZ (meteo.hr), Split Marjan station, 1948–2024.
The 1971–2000 normals put September at 15.4 warm days rather than 17, because they cover a different and shorter period. Both are real; they are not interchangeable and are never shown in the same table here. The shape is identical either way, and the shape is the argument: whatever the exact count, September has it and October does not.
17 vs 1
Days above 25°C at Split Marjan in September and October, 1948–2024.
What is running, and what it costs
The tariff season runs to 27 September on every line checked, so almost the whole of September is bought at high-season prices. The timetable has already come off its peak: line 634 dropped from 22 sailings a day to 20 on 31 August, and line 9807's full route to Korčula and Polače ended on 30 August. Line 602 to Vis holds three sailings a day only to 20 September.
Waiting until late September for cheaper crossings
The fare does not move until 28 September. A trip timed for the third week of September pays exactly the same €52.00 for a car under 5 m to Vis as one in the second week of August, while getting a shoulder timetable rather than a peak one.
The genuine bargain is the last days of September and the first of October, when the off-season tariff has returned and the sea at Split is still 19.3°C. That window is four or five days wide and nobody advertises it. See October for what happens next.
Where September works best
The further south, the longer September holds. Dubrovnik keeps 16.7 warm days and 10.3 hours of sun; Rijeka keeps 10.4 warm days and 6.7 hours. If September is the month, the trip wants to be in southern Dalmatia rather than Kvarner or Istria. Dubrovnik and Hvar are the two bases that lose least.
What to decide before you book
- You are choosing between June and September. September's sea is warmer at all three measured stations.
- You are choosing between August and September. You trade 13 warm days for a sea that is only 1.9°C cooler.
- You want the fare to drop. It does not until 28 September. Nothing before that date is off-season.
- You are going north. Rijeka keeps 10.4 warm days against Dubrovnik's 16.7. Go south instead.
Find September flights and hotels
What do you need to work out next?
September is the strongest shoulder month. These decide how much of it you get.
Where to stay
Does the south hold September better?
Dubrovnik keeps 16.7 warm days and 10.3 hours of sun a day.
Getting around
Which sailings have already been cut?
Line 634 dropped from 22 to 20 a day on 31 August.
When to go
How fast does it end?
Seventeen days above 25°C in September; one in October, on the same record.
Planning
How do you route a September week?
The water is still 21.7°C at Split, so the coast is still the point.
Climate data: DHMZ (meteo.hr), climate normals 1971–2000. Climate data: DHMZ (meteo.hr), Split Marjan station, 1948–2024. Ferry data: Agencija za obalni linijski pomorski promet (ZOLPP), 2026 state coastal line register and per-line timetables.