Sea tornadoes in the Adriatic

An increasingly common meteorological phenomenon, the sea tornado, is occurring off the coast of Croatia. Let's explore how it forms, what to do if you encounter one, and whether it's as dangerous as it appears.

No matter whether you call it a sea twister, waterspout, or wind vortex, it's important to understand what it is. From afar, it appears as a dark, swirling funnel connecting the water’s surface to the sky, typically forming over large bodies of water like seas or lakes. 

Waterspouts most often form beneath storm clouds, particularly when the atmosphere is unstable. Warm, moist air rises from the water’s surface and, upon meeting cooler air, begins to rotate. These tornadoes are often associated with supercells, which are types of storms that contain rotating updrafts. Witnesses have reported that these waterspouts can rise to heights of approximately 20 to 40 metres.

The duration that a waterspout lingers on the sea surface can vary, but according to witnesses, it typically lasts between 10 and 30 minutes.

Although waterspouts are generally considered less dangerous than land tornadoes, they still deserve caution. Swimmers are most at risk, as an encounter can be fatal, but boats should also be on alert. There have been cases where small vessels were blown several kilometres by these wind vortices. In general, if a storm is in the forecast, it’s safest to seek shelter in a nearby harbour or bay and avoid sailing.

Predicting whether a storm will develop into a waterspout is very difficult. However, most weather forecasting models and apps, like Windy, can detect storms. As a precaution, if you see a storm in the forecast, you should prepare for potentially dangerous conditions such as waterspouts, high winds, and rough waves, which can be hazardous or at least uncomfortable for vessels and their crew. When reading a wind forecast chart, pay attention to atmospheric rotations and rapid shifts in wind direction, as these could signal the development of a tornado.

Ideally, you should avoid coming into close contact with a waterspout. If your forecast app shows a risk of thunderstorms or a possible waterspout, seek shelter in a safe cove and ensure your boat is securely tied down. Clear the deck of any loose items like drying clothes, paddleboards, or glasses, and secure the hold to prevent dangerous movement of loose objects. Make sure cabin doors are locked, and check the sails so they’re ready for use if necessary.

If you’re forced to navigate near a waterspout, position your boat so the bow faces the oncoming waves and wind, which can help minimize the risk of damage. Carefully reduce speed to lessen the impact of waves.

If you find yourself directly in a waterspout with your sailboat, our skipper Jacob advises to reef the headsail to the smallest size possible (like a handkerchief) and endure the intense two minutes of chaos.

In mid-September 2024, a waterspout appeared in the area between Šibenik, Rogoznica, Zadar, Vodice, Primošten, and Žirje. The waterspout was moving quickly, and sailors reported sightings across the region. Fortunately, based on available reports, there were no injuries or loss of life.

Back in June 2013, the Pula area witnessed an extraordinary number of waterspouts. According to witnesses, as many as 20 vortices filled the sky, creating a dramatic and rare spectacle.