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The fact that the north Adriatic almost touches the Alps causes certain climatic differences between the north and the south Adriatic coast. They are not so visible during the summer, but in the winter the weather pictures of the north and the south are often very different. The borders between the two faces of the same sea are very clear - it's cape Ploca, known between the sailors as Punta Planka, two miles south from Rogoznica, on the rout to Šibenik on the way to Split.
Cyclones and Anticyclones
Weather changes on the Adriatic dictates the changes of cyclones and anticyclones over the middle and South Europe. The usual travelling 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.
This rhythm of change is usual for the Adriatic, and it differs only by how often and from where do the cyclones come. In the summer they are rear and they travel mostly north of Adriatic, in the winter they are more powerful and dipper. They travel one after the other from the Geneva Bay and Triennia Sea, through south Italy over to south Adriatic and further to the southeast.
The differences between summer and winter
In the Summer the differences between the north and south are much smaller- both sides of the Adriatic are combined into one climate territory with a lot of warm and sunny days, high daily temperatures which get softened by a pleasant landward breeze, low percentage of humidity and not to hot nights. The temperature of the sea surface is between 24°C and 26°C on the entire Adriatic. At the end of the summer the differences between the north and the south Adriatic become more noticeable during the nights, while the daily temperatures are pretty much the same. Colder nights soon lead to differences in the sea temperatures. In the beginning of September the sea starts to get colder. On the north the sea temperature falls to 18°C and more, but on the South it can still be 22°C. The air temperature during the winter is different as well. In the Trieste Bay and under the Velebit the snow carried by a strong storm is not so rear, while at the same time on Hvar, Vis and Koreula the weather can be very pleasant. Especially during the winter, cape Ploca proves to be worthy of its name - the climate border - very often two types of weather are fighting over it.
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 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. It is strongest in the Velebit Channel and the Gulf of Trieste. 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.
For smaller boats it can be very unpleasant. Without it the Adriatic, especially the north part, would be much more pleasant Rarely it blows more than 3 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. As it brings cold and heavy air, it finds it's way towards the sea through the mountains. That's why it's best to hide from it in the bays underneath the mountains.
The South wind
It is the warm wind from the southeast (in Croatia called "jugo" or "sirocco") it blows through the Adriatic, during the cyclone it brings clouds and rain. The air pressure falls. It develops slowly; usually you can notice it two or three days before. 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. Between March and June it blows in the north as well. During the winter even longer. There are also, so-called dry south winds, they last longer, do not bring rain, but can be powerful as a storm.
The north - western wind (in Croatia called "Maestral") is a local 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.
The north-easterly wind (in Croatia called ''Burin'') blows in the summer from the mainland.
The northerly wind (in Croatia called ''Tramontana'') is a type of bora.
Another type of bora is the easterly wind ''Levante''. From west blows ''Pulenat'' and from south-west ''Lebic''.
The landward breeze
That's a good wind, friendly to sailors, and pretty much to every one who enjoys the summer sea because it softens the heat. It's a daily thermal northeast wind. It's very usual from spring to fall, and the strongest in July and August.
It usually starts around 9 or 10 in the morning. It gets the most powerful in the afternoon, and it ends with sunset.
It's usually weaker on the north Adriatic than on the south, where in the canals between islands it's force can get unpleasant for small boats.
Sudden storm (called "Nevere")
Next to the north-eastern the sudden storm on the Adriatic is possibly the most unpleasant experience, especially for small boats. 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.
Forecasts giving the present state and likely development of the weather are given in regular bulletins or by radiotelephone.
Radio forecasts. These begin with a description of the weather (i.e. wind 7 Bf freshening, sea 5 increasing, fog etc.); this is followed by the general situation and forecast for the next 12 and 24 hours in the Adriatic and Otranto. Coastal radio-stations RIJEKA RADIO, SPLIT RADIO, DUBROVNIK RADIO give forecasts three times a day in the national language followed by English. Other important radio-stations are MALTA RADIO, TRIESTE RADIO and the Italian RAI service.
Special warnings are transmitted as soon as storms or other weather conditions are expected and these are repeated following the next period of radio silence.
The present situation and forecast can be provided for smaller sections (sectors/quadrants) given by name on separate map (index map).
The Croatian naval meteorological service divides the Adriatic into northern, central and southern.
Weather (meteorological) bulletins provide weather charts with meteorological tables for places on the Croatian coast, details of synoptic situation, weather forecasts. They may be obtained from harbour master's offices or by NAVTEX (radio-telefax).
Maritime Meteorological Centre in Split provides weather information over the telephone and radiotelephone.
Weather reports are broadcast on these channels at the following times (UTC):
Rijeka Radio VHF (channel 24): 0535, 1435 and 1935
Split Radio VHF (channels 07, 21, 23, 28): 0545, 1245 and 1945
Dubrovnik Radio VHF (channels 04, 07): 0625, 1320 and 2120
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