The Adriatic Sea
The Adriatic is the northernmost part of the Mediterranean Sea. It extends from the Strait of Otranto (where it connects to the Ionian Sea) to the northwest where it ends at the Veneto region in Italy. There are over 1,300 islands in the Adriatic and most of them are located along the Croatian coast.
The Adriatic is basically divided into three basins. The shallowest is located in Istria, where the depth does not exceed 50 metres. Moving south from Pula, the seabed mildly drops, making a long, narrow valley which extends from Žirje towards Italy. The biggest depth there is about 240 metres. From there, the bottom rises to Palagruža reef, where the depth does not exceed 130 metres. Towards the south, the bottom drops steeply towards the South Adriatic basin, where the biggest measured depth is 1,233 metres.
The appearance of the underwater relief is a result of tectonic movements, abrasion or erosion that have happened several million years ago, in times when certain parts of the seabed were land or the coastal area. Uneven areas on the bottom are constantly reduced by sedimentation of detritus from the land. This process is rather slow, but constant. The configuration of the seabed provides perfect conditions for the Adriatic’s rich and versatile flora and for you to explore.
The high and low tides have relatively small amplitudes in the Adriatic. In the southern part, the difference is rarely above some forty centimetres, while in the northern part it is somewhat bigger, so that it comes to 1 metre in Istria and the Gulf of Trieste. In some narrow channels and bays, the high tide can grow considerably during a strong sirocco. That phenomenon is characteristic for big and deep bays of the southern Adriatic. The tides are of a mixed type, which means that their rhythm is semidiurnal during the new and full moon and of a daily type during the first and the last quarter of the day. Their amplitudes are very irregular.
Sea currents occur under the influence of winds, the difference in pressure, temperature, and the differences in salinity. With respect to the direction, they can be horizontal or vertical. There are also bottom currents, which appear as the consequence of moving of water from warmer areas to colder ones, during which the surface layer gets cold and descends towards the seabed. Currents are weakly observable in the Adriatic. Their speed changes in particular areas, but it also depends on time periods. The prevailing currents in the Adriatic flow counter clockwise from the Strait of Otranto to north, along the Croatian coast and back south along the Italian coast. The average speed of currents in the Adriatic is about 0.5 knots.
Salinity of the Sea
The total quantity of salt dissolved in one kilogram of sea water is called salinity. It is usually expressed in permillage. The salinity of the Adriatic Sea is 38.30 per mill averagely, i.e. there is 38.30 g of salt dissolved in 1 kg of water. In the northern part of the Adriatic, the salinity is somewhat lower than in the middle and southern part because of the influence of the Po River. The salinity in the Adriatic is lower than in the Mediterranean as the Adriatic collects a third of the fresh water flowing into the Mediterranean.
The annual changes in sea surface temperatures are quite significant in the Adriatic. The average annual temperature is 17.5°C. During the winter, the sea is the coldest and the average surface temperature drops to 11°C, but it can drop to about 7°C or lower in rare occasions. In the spring, the sea becomes warmer and the surface temperature rises to 18°C. In the summer the surface of the sea reaches a high average temperature of 22 to 25°C, and in the southern Adriatic and Istria up to 27°C.
Parts of the water column that have same temperature, the thermoclines, are well distinguished in the Adriatic. These thermoclines are most evident in the summer months. We can notice the first thermocline at the depth of 3 to 5 metres, the next one is at about 12 metres and yet another one at 18 metres, while below 30 metres the temperature is mostly constant throughout the year. In the winter, the sea temperature tends to be the same throughout the water column.
Waves in the Adriatic
Waves occur primarily as a result of wind. The bigger the reach, i.e. the surface across which the wind blows, the higher the waves will be. The Croatian coast with its numerous islands reduces the reach and that means that the waves stay relatively small and the sailing is safe and pleasant. Most often, heights of waves in the Adriatic are between 0.5 and 1.5 metres, and they very rarely exceed 5 metres in the open sea during the winter.
Weather in Croatia
Climate and weather conditions
The climate at the Adriatic is typically Mediterranean, with mild rainy winters, and hot and dry summers. The air temperature changes depending on the area. Thus, summer temperatures in July can rise up to 34°C in the northern part, while in the southern part they can rise even to 38°C. In the winter, the coldest temperatures are noticed in the northern Adriatic (even up to -16°C), while they will not have exceeded +6°C in the southern part.
Weather conditions in the Adriatic are affected by the general weather situation in the Mediterranean and local climate conditions. Generally speaking, light to moderate winds with few storms prevail until June. In July and August, a period of calm sets in and storms are more frequent. From September on winds are again stronger.
The bura (bora) and the jugo (scirocco) are the main winds on the Adriatic. They prevail in the winter period from September to May. The prevailing wind in the summer is the maestral.
The bura is a cold and dry north-easterly wind. It blows from the continent, i.e. from the eastern side of the Adriatic towards the open sea and brings bright weather. It starts abruptly and blows in squalls toward the sea. It is strongest in the Velebit Channel and the Gulf of Trieste. Picture shows typical "bura" corridors: (1) Golf of Trieste, (2) Kvarner, (3) Velebit Channel, (4) Sibenik, (5) Split - Makarska, (6) Peljesac and (7) Dubrovnik. In the summer the bora blows as a local wind and lasts only a few days. In the winter it may continue for up to two weeks.
The jugo is a warm, humid east-southeast wind. It is accompanied by heavy clouds and rain. It is not a sudden wind like the bora as it takes 36-38 hours to develop. It blows throughout the Adriatic. In the summer it may appear as a local wind and is more frequent in the southern part of the Adriatic. Between March and June it blows in the north Adriatic as well.
The maestral is a local westerly wind which blows from the sea, mostly in the summer. It usually starts between 10 and 11 in the morning and reaches its greatest strength between 2 and 3 in the afternoon to die down at sunset. It brings good weather. It is usually accompanied by white clouds. While bura and jugo each in their own way offer sailors the excitement and challenge, maestral guarantees a pure pleasure during which you can give yourself to the sea without fear.
The burin, a north-easterly, blows in the summer from the mainland, usually in the morning. The tramontana is a type of bora; it is a northerly. Another type of bora is the easterly levante. Pulenat blows from west and lebić from south-west. The nevera, a violent westerly, comes as a storm or squall. In the summer months, storms in the Adriatic are sudden and violent and produce a short-lasting swell. The Adriatic storms have an advantage: they do not last long and some of them leave behind pleasantly cool air. During periods of high pressure, the Adriatic also has the classical rhythm of winds: winds from the land during the night and from the sea during the day.
The coastal radio stations broadcast weather reports in Croatian and English several times a day. The reports include a general weather situation report, messages and the forecast for the following 24 hours. Weather reports are broadcasted at the following UTC times (UTC + 1 h = CET; CET + 1 h = CE summer time):
- Rijeka Radio VHF Channel 24 – 05:35, 14:35, 19:35
- Split Radio VHF Channels 21, 23, 07, 28 – 05:45, 12:45, 19:45
- Dubrovnik Radio VHF Channels 04, 07 – 06:25, 13:20, 21:20