WEATHER IN CROATIA
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 is 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.
The air temperature in winter months is between 5 and 10° C (41-50° F) and the sea temperature are in average 12 ° C (54 ° C).
SEA CHANGES, CURRENT AND WAVES
The changes of high and low tide in the Adriatic are small and don't effect the safety of the sail. On the south the difference between the tides is rarely higher then 40cm, but as you approach the North the amplitudes will become bigger - around Istra and Trieste Bay the middle extreme amplitude is almost 1m. 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 harbours. This is very rear (more often in the winter), and it's characteristic for the big and deep bays of the south Adriatic. During south winds the tides are usually higher, and during storms the sea is lower than the average. 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.
The waves in the Adriatic are not as high as the ones in the oceans, but that does not mean that they can't be unpleasant for smaller boats. The south wind creates bigger waves then northeastern wind (the biggest measured south wind wave was 10,8m, and the north-eastern 7,2m), but still it would be wrong to presume how the south wind waves are more dangerous because they are bigger. On the contrary, northeastern wind waves are shorter by half, but still shaped unsymmetrical, which means that the boat will suffer more in the waves of the northeastern wind. The landward wind waves get pretty high on the South, it can get up to 4m of height.
THE WINDS OF THE ADRIATIC
The entire east side of the Adriatic has it's own weather changes, especially the winds. Since the old days fisherman could read the small signs of nature and know what the sky is preparing next. That's why you cant make a mistake by asking a fisherman what's the weather going to be like in the evening or the next day and where is the best place to anchor for the night.
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, Šibenik, cape Ploča, bay of Vrulje (between Omiš and Makarska), Trstenik bay on peninsula of Pelješac.
Levanat from the east is a wind comparable to Bura, but not so often.
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 (south-west), Ostro (south)
These winds present variations of the Jugo wind (SE), and have similar characteristics.
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 on the southern part of Adriatic. Away from the coast it gets stronger and creates bigger waves.
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 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 it's 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 where caught by the storm totally unready.