Cold fronts

A cold front is represented by a blue line with triangles oriented in the direction of the front movement. A cold front represents the leading edge of a cold air mass that pushes it way under a warmer, lighter air mass, forcing it to rise rapidly, as a bulldozer effect. This rising motion often creates towering clouds, showers, or thunderstorms, especially if the warm air is moist. As the front passes, there's typically a sudden drop in temperature, a sharp wind shift (often veering), and a quick rise in air pressure. Cold fronts usually move fast and bring abrupt, sometimes violent weather changes, making them especially important for sailors to anticipate. Wind can shift from SE (Jugo) to W or NW in Bora situations.

Example of a cold front moving over England and Britany on 14 July 2025

Warm fronts

A warm front is the leading edge of a warm, lighter air mass that slowly rises over a retreating cold air mass. Because the warm air ascends gradually, it forms layered clouds (starting with high cirrus and thickening to stratus), often bringing steady rain or drizzle over a long period. The approach of a warm front is marked by a slow drop in pressure, increasing humidity, and winds that back (e.g., from east to southeast). After the front passes, temperatures rise gently, the rain eases, and pressure stabilizes or rises slowly. Warm fronts usually move slowly and bring more subtle but prolonged weather changes than cold fronts.

Example of a warm front moving eastward across Ireland, https://meteo.hr/prognoze_e.php?section=prognoze_model&param=web_fronte_sutra12

When a warm front passes, the changes are more gradual and subtle than with a cold front, but they still can have a big impact on sailing... 

Mesoscale drivers, understanding regional weather drivers in the Northern Adriatic

When the synoptic map shows nothing special, the real action often comes from local and regional weather drivers.

In the Northern Adriatic, weather conditions are often influenced not just by global and synoptic patterns but by mesoscale drivers, regional-scale systems that operate over tens to hundreds of kilometres. These drivers can change wind strength and direction dramatically over just a few hours or even minutes, especially near coastlines and islands.

Understanding these mesoscale effects is essential for safe and comfortable sailing in this highly variable and geographically complex region.

40 knots bora katabatic wind in Senj, while only 10 knots in Mali-Lošinj, 

from Northeast over the Triest and Senj area on 9 June 2025.

---

1. Sea breeze and land breeze cycles

Sea breeze (daytime)

• Driven by temperature contrast between land (which heats faster) and sea.
• Warm air over land rises; cooler, denser air from the sea rushes in to replace it.
• Typically builds late morning, peaks in the afternoon (10-20 knots), and fades around sunset.
• Most reliable in spring and summer, during clear-sky high-pressure conditions.

Land breeze (nighttime)

• Land cools faster than sea after sunset.
• Cold air over land flows out to sea, usually as a light offshore wind (less than 10 knots).
• Can oppose or reinforce synoptic winds depending on alignment.
• Watch out: the transition period around sunset and sunrise can be tricky, especially when sea breeze fights against a light synoptic wind.

Caution: can result in 180° shift in wind direction, to take into account when anchoring in a small cove.

---

2. Mountain and valley winds

The Dinaric Alps and surrounding terrain create downslope (katabatic) and upslope (anabatic) flows:

Katabatic winds

• Cold, dense air descends rapidly down mountain slopes.
• Strengthens at night, especially during Bora events.
• Can cause sudden gusts even when synoptic maps show calm conditions.

Anabatic winds

• Sun heats mountain slopes during the day.
• Warm air rises, sometimes enhancing cloud formation over inland hills.
• Can trigger localised convection, cumulus development, or instability.

Example: inland hills east of Trieste can enhance the afternoon sea breeze or destabilize conditions.

---

3. Thunderstorms and squall lines ("nevera")

In summer, especially from June to September, the Adriatic is prone to rapidly forming convective storms:

• Triggered by hot, moist surface air meeting a cold air mass aloft or by convergence zones.
• Typically form in late afternoon or evening and may come from the northwest, crossing from Italy or forming over Istria.
• Nevera: sudden violent squall line, short-lived but dangerous. Winds can spike to 30+ knots with thunder, lightning, and downbursts (see "Never ever again unprepared for Nevera, 16 June, Šibenik").

Caution: nevera often form under clear skies and may not be well-flagged by forecasts.

Synoptic scale: understanding global weather drivers

Understanding weather begins at the global level, what meteorologists call the synoptic scale. The word "synoptic" comes from Greek and means "seen together" or "comprehensive." In meteorology, it refers to large-scale atmospheric patterns and interactions that influence the weather over wide areas.

Figure 1: synoptic chart over the Atlantic ocean and Europe, 6 August 2025

Synoptic scale level is the first level to consider when assessing weather before heading at sea. It gives an overview of the large scale drivers such as high and low pressure areas, front positions, clouds, winds, air and sea temperatures...

Setting the global picture: how air moves around the earth

“To understand what’s going to happen next in your sailing spot, you need to know what’s happening around the world.”

When planning a sailing trip, particularly in the relatively enclosed Adriatic, knowing where the wind comes from, where it might go next and what will be the drivers is vital. Most of the winds we experience aren't just random gusts. They are part of a much larger earth’s atmospheric circulation.

Figure 1. Idealised depiction (at equinox) of large-scale atmospheric circulation on Earth, Wikipedia

This post explores how the global engine of wind and weather works, and why it matters every time you raise your sails...

Adriatic weather forecast sites

This page is a compilation of links that I use to explore the weather situation in Northern Adriatic.

Belisama in Limfjord, 20-21 July 2025

As part of or summer explorations, we decided to explore the Limfjord with a couple of South-African friends on a weekend where all conditions could be met: none of us four having to work and weather permitting. The ride from Marina Polesana is 27 nautical miles, heading north through Fažana and Rovinj, before heading up the Limfjord. 

Our Australian friends were there for a couple of days last year after we met in Umag and they were advising us to visit this place. And we did and understood why...

Portić - Borovinje, 4th July, 2025

Borovinje is a large cove that is only partially protected from the Bora wind. One sailor on Navily mentioned a strong funnelling effect under the Bora wind, which results in strong gusts of wind. We experienced these gusts all night long!

And this exactly what we got overnight... But before that, it had been a paradise!

Polesana - Uvala Portić, 3 July 2025

Uvala Pović is a large bay for anchorage which is very famous fo sailors all over Istria. Even at the peak of the season, in July, it is easy to find a spot, in particular if you want to come close to the Shore in the 4 to 6 metres depth, a draft still ok for most boats, but in particular for OVNIs as Belisama, that needs only 1.05 m...

So far, in her new module, Kaja painted from the land, but the challenge this time is eventually to paint from the sea! So that is why we left for the possibly best spot for paintings cliffs in Croatia, from the Kamenljak bay...

Unije, 26 June, the last stop before crossing the Kvarner back to Pula.

Unije is a small, tranquil island in the northern Adriatic, part of Croatia’s Cres-Lošinj archipelago. Known for its unspoiled nature and crystal-clear waters, Unije is ideal for swimming, walking, and relaxing. The island is popular with sailors for its sheltered anchorages protected from Bora winds, especially on Thursday nights as rental boats need to be back to Pula on Fridays. 

Thursday afternoon in Unije, at peak season...

A stop-over in Losinj, 24-25 June

The island of Lošinj, located in the Kvarner Gulf, has long served as an important center of maritime activity. Its scenic landscape and naturally sheltered bay, protected from all winds, have made it a favoured stopover since ancient times, particularly in light of the Bora winds that frequently affect this northern part of the Adriatic Sea.

Belisama in Mali Losinj marina

And indeed, it has a lot to offer...

A night in Zavratnica cove, 22 June

We spent the shortest night of the year in Zavratnica (pronounce Zavratnitsa) cove, a well preserved secret 40 km south of Senj, along the Dalmatian coast. We were advised by my cousins who explored the coast in a camping car and with whom we sailed to the Kornati (see earlier posts). 

Belisama in the Zavratnica cove, from the trail to Jablanac

This place is documented in Navily, the community forum for sailors looking for anchorages...

A night ride to Rab, 20-21 June

With the need to return to Pula by the end of the week—and a forecasted storm approaching—we decided on a one-shot night sail from Šibenik to Rab, a 90-nautical-mile passage. Our decision was guided by the forecast of a moderate Bora event, with wind speeds around 14 m/s (28 knots), which we expected would allow us to maintain a steady 7 to 8 knots under sail, significantly shortening the time needed to cover the distance.

Passing Sibenik at night

It worked as expected: under two reefs and the staysail, we made good speed through the night. However, the Bora lasted much longer than anticipated, extending well into the next day. While the boat handled the conditions well, the prolonged exposure to strong winds and confused seas made for a demanding passage...

Krka National park, 18-19 June

Krka National Park (pronounced Queurka in French) is located just a few miles upstream along the Krka River from the coastal city of Šibenik. It stands out as one of Croatia’s most popular and scenic national parks, and it’s well worth a visit—whether you're arriving by sailboat or exploring by land. The park’s highlight is Skradinski Buk, a breathtaking series of travertine waterfalls and emerald pools cascading through a lush, forested canyon. It's one of the most iconic natural sites in the country. For sailors, the town quay in Skradin offers mooring at a rate of €5 per meter plus 25% VAT—about half the price of the nearby ACI Marina. Entry to the park during the summer season is €40 per person, but the experience is undeniably worth the cost. Don’t hesitate—Krka National Park is a must-see destination on any Croatian itinerary.

The Skradinski Buk, the most famous spot in the park

Getting there by sailing boat from Šibenik is a very nice 4 nm ride through the Krka river...

Šibenik, the Magnifique, 17-18 June

Šibenik is one of the oldest towns on the Adriatic Sea, at the mouth of the Krka River where it meets the Adriatic. Over the centuries, Šibenik developed under the Croatian kings before falling under Venetian and later Habsburg control, with a French period in between, from 1809 to 1813, each leaving architectural and cultural legacies. The city is best known for its medieval fortresses and the UNESCO-listed Cathedral of St. James, an architectural masterpiece blending Gothic and Renaissance styles. With its compact stone streets, strategic location, and deep natural harbour, Šibenik played a key role in regional history, serving as both a political centre and a defensive stronghold. Today, while its trade function has diminished in favour of tourism and cultural heritage, the city retains its historic significance and continues to serve as a gateway for regional economic and maritime activity in the Adriatic.

Šibenik, along the Krka river, with the connection to the Adriatic sea in the background

We got a berth at the quay in the centre of the town. Most convenient en enjoyable! From there we could go shopping after our four around the Kornati using Uber.

And we were at the right spot. to visit the town centre...

Never ever again unprepared for Nevera, 16 June, Šibenik

I thought we were familiar with most of the winds that sweep across the northern Adriatic, but last night we were caught off guard by a Nevera — one of those sudden Adriatic storms that strike without warning and vanish just as quickly. In less than two hours, over 30 boats were driven ashore, and rescue services were responding to incidents all along the northern coastline of Croatia.

Picture south of Rovinj by A. Simunović

Let me tell you what happened to us...

Four days in the Kornati islands, 12-15 June

The Kornati National Park, located in central Dalmatia, is an uninhabited archipelago comprising 89 islands, islets, and reefs spreading across crystal-clear waters. It is a paradise for sailors with lots of anchorages in protected coves. 

View to the Northwest from Fort Tureta on Kornat island

After picking our cousins from France in Murter, we engage in an exploratory tour of the Kornati islands...

Velebit canal, ahead of the Bora, 8 June

 The Velebit Channel is a unique place, stretching south-easterly from Senj in the north to Rovanska in the south. The Velebit mountain range borders it along the coast, and the long, narrow Pag island borders it on the seaside..

Sailing close-hauled in the Velebit, but with wind coming from the sea, therefore, not Bora!

The Velebit Channel is famous because of the katabatic wind it generates, known as the bora. Given that an episode of Bora is expected tomorrow, we rush through the canal and prolong our ride of a few miles to avoid its effects!

Goli otok, 6-7 June 2025

The aerial view of Goli Otok makes it clear why its name translates into English as "Barren Island" and into French as l’Île Nue. We spent two nights there in the square-shaped harbour to visit the island.

Goli Otok was an internment camp established in 1949 in the aftermath of the Tito–Stalin split. Tito, who became Prime Minister of Yugoslavia in 1945, sought a more independent and regionally influential role for Yugoslav communists, particularly in relation to neighbouring countries such as Albania, Greece, and Bulgaria—an ambition Stalin did not support. Tensions culminated in 1948 when the Communist Information Bureau (Cominform) issued a resolution calling for a change of leadership in Yugoslavia. This led to a rift between Tito’s Yugoslav communists and the pro-Stalin Cominformists.

The Yugoslav communists retained power and established a system of camps and prisons to detain Cominform supporters—the largest of which was the Goli Otok camp, opened in July 1949.

Image source: Republic of Croatia State Geodetic Administration

Today, the island is abandoned and slowly being reclaimed by nature. Yet, Croatians remain acutely aware of their history and the crises that have shaped it—reaching a peak during the Balkan wars of the early 1990s.

Let's have a tour...

Start of the summer sailing, 4 June

 With both of us officially on vacation starting end of May, we took a few days to get the boat ready for a month tour of Croatia. In particular, it was rather difficult to get new parachute flares as regulation requires some special pyrotechnic closet in shops, and none of the ship chandlers contacted in Pula could get any! We finally got them from Rijeka.

On 4 June, late afternoon, we depart from Oula for Banjole, a few miles out. Night at anchor.

Sunrise in Banjole, 5 June

Start of the 2025 season: Pula to Pula through Cres, Krk and Losinj (172 nm)

May 6 - 10, a practice with a crew of newly licensed sailors

This year the season started on the 6th of May with a request from motivated nephews to "experience" sailing after having obtained their sailing licence the year before, the idea being to go through all waters and weather conditions. And the crew got it, because May is the right time to experience unstable weather conditions, associating warm spring days driven by breezes and cold days driven by Bora (catabatic winds) and Yugo! We got it all!

The crew, May 6, departing from Pula