The Croatian side of Adriatic has a Mediterranean climate, bringing it on average 2600 hours of sunshine per year.
During the summer, the average seawater temperature can be 24 – 27 degrees Celsius. The warmest months are July and August when the air temperature is between 25°C and 35°C (77°F - 95°F) and the sea temperature reaches up to 28°C (83°F). The rain is very rare. This is the time when most of the tourists come.
If you're for a quieter time at the beach and not so many tourists, maybe June and September are months for you. They are also very warm months with average temperatures around 25°C (77°F) and the sea surface temps between 20°C and 25°C (68°F - 77°F). Sunbathing and swimming are also possible in April, May, and October, but it really depends on the weather and chances are that you'll get more sunshine in the southern Adriatic. In that period expect temperature between 15°C and 25°C (59° F - 77°F) and the sea temperature between 16 and 21°C (61 - 70°F). This is a period with more rain and windy days.
In general, the weather conditions in the Adriatic Sea area can be rather unpredictable. Winds can literally change in opposite directions in minutes. It is very important to monitor the weather forecasts. Weather changes on the Adriatic are dictated by the changes of cyclones and anticyclones over the middle and South Europe. The usual traveling way of cyclones over the Adriatic is from west to east. On their front side they bring winds from the south with warm and moist air, so the weather is cloudy and rainy. Behind the cyclone with the growing of anticyclone and it's spreading over the European land through the east, the wind moves to the north-east and brings cold and dry air, north-eastern wind chases the clouds, which stabilizes the weather. Until the arrival of the new cyclone, the weather stays sunny and calm, with a daily landward breeze during the summer.
During the summer, cyclones are rarer. They usually pass further north across the European mainland. This leads to only small differences in weather conditions along the Croatian coast. The changes of the high and low tide in the Adriatic are small and they generally don't affect the safety of the sail. On the south, the difference between the tides is rarely higher than 40 cm, but as you approach the North the amplitudes will become bigger - around Istria and Trieste Bay the middle extreme amplitude is almost 1 m. However, during the long lasting and strong south winds in some narrow canals and bays the tide can grow so big that it can flood over walls on the beaches in harbors. This is very rare. The atmosphere pressure has a big impact on them as well. Sea currents are small, and present no problem during the navigation. But you still have to keep them in mind, especially in some narrow canals, where they can get up to 4 knots of speed.
Bora NE - As a cold wind, the north-eastern (in Croatia called 'bura') is blowing from the continent, 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. For sailors, this wind is very unreliable: she comes suddenly and with heavy gusts. In the summer blows as a local wind and then lasts only a few days. In the winter it may continue for six to fourteen days. When it's local it can start and stop within 24 hours, but if it's wide and continental it can last the entire week, and in that period it gets weaker or stronger a couple of times. Sudden starting of the wind is one of its most dangerous sides, especially for less experienced sailors. At the coast, it can easily reach 40 - 50 knots, during the winter even more. Usually, she precedes clear weather, but during the Bura conditions get foggy because of foam and water drops carried by the strong winds. Bura is the strongest in Gulf of Trieste, Kvarner (near Krk), Velebit channel, Nin bay, Sibenik, cape Ploča, a bay of Vrulje (between Omiš and Makarska), Trstenik bay on a peninsula of Peljesac.
Levant E - Levanat from the east is a wind comparable to Bura, but not so often.
Jugo SE - In Croatia called "Jugo" or "Sirocco" is a warm, moist, south-easterly wind. It blows through the Adriatic, during the cyclone it brings clouds and rain. The air pressure falls. It develops slowly; Jugo can blow from ESE SSE directions, and then it can be very powerful, with big waves and low clouds, and usually a lot of rain. There are also, so-called dry south winds, they last longer, do not bring rain, but can be powerful as a storm. It is not a 'sudden' wind like Bura, but it develops gradually over a 24 – 36 hour period. As it blows through the canal, it produces high, but long waves. It usually lasts much longer than the north-eastern wind, five to seven days. In the summer it may appear as a local wind and is more frequent in the southern part of the Adriatic.
Lebic SW, Ostro S - These winds present variations of the Jugo wind (SE) and have similar characteristics.
Tramontana N - Tramontana blows from the north, but sometimes, locally can blow from NNW. It is similar to Bura, but usually, not as wild and strong. It is a local and dry wind that brings cold air. Usually, it blows from 15-25 knots. It brings bright skies and high pressure. It is more common in the southern part of Adriatic. Away from the coast it gets stronger and creates bigger waves.
Maestral NW - Maestral is a typical summer wind, caused by the temperature differences of land mass and the sea, and it blows from the north-west. It starts during the morning (around 11:00 AM), and it gradually builds up until the 4 PM, dying towards the sunset. It is a moderate wind, and it brings beautiful weather and white clouds.
Burin NE- Burin is also a typical summer wind, like Maestral, but it blows during the night from the opposite direction, from the north-east, and it is also a moderate wind, a light breeze usually. It can start with the sunset, and continue until the sunrise when it is the strongest. Burin brings nice weather.
Nevera (A SUDDEN STORM) - Next to the north-eastern the sudden storm on the Adriatic is possibly the most unpleasant experience. They are thermal storms that come speeding from the west, from the open sea; they last short but have great force. They are the most often in the summer, and they get very powerful as fall comes. On the smallest sign of the storm you should, with no delay, take every precaution, because the time is short. If there is any possibility of getting away from its way, you should. Before the storm starts it's totally quiet, and often in the last minutes before it breaks a breeze blows, very shortly towards the storm - it makes it impossible to hear the sounds of thunder, that's why a lot of people were caught by the storm totally unready.