Europe does not typically experience true tropical hurricanes due to unfavorable geographical and meteorological factors. While largely shielded from these powerful systems, the continent is regularly impacted by their remnants, which still bring significant weather events. These post-tropical cyclones arrive after undergoing a crucial transformation that changes their structure and energy source. The storms that affect European shores are typically intense non-tropical systems or the final stages of a former hurricane that has crossed the Atlantic.
Defining the Difference Between Tropical and Extratropical Cyclones
The distinction between a true hurricane and the storms that strike Europe lies in their internal structure and power source. Tropical cyclones, called hurricanes in the Atlantic basin, are characterized by a warm core structure. This means the air temperature at the storm’s center is warmer than the surrounding atmosphere. They are driven by the release of latent heat energy from condensing water vapor above warm ocean waters.
An extratropical cyclone, the type that regularly affects Europe, has a cold core structure. These systems draw energy from horizontal temperature gradients in the atmosphere, a process known as baroclinic instability. Extratropical cyclones are larger and contain weather fronts, which are absent in a tropical hurricane. The term “hurricane” is scientifically inappropriate for the severe windstorms that impact Europe, as they are products of mid-latitude atmospheric dynamics.
The Environmental Factors That Limit Hurricane Formation Near Europe
The primary obstacle preventing tropical hurricanes from forming or surviving near Europe is the lack of sufficiently warm ocean water. A tropical cyclone requires sea surface temperatures (SST) of at least 26.5 degrees Celsius (80 degrees Fahrenheit) extending through a deep layer of the ocean. The North Atlantic near Europe, even during peak season, is generally too cool to provide the necessary energy. Any storm tracking north toward Europe inevitably moves over these cooler waters, cutting off its primary heat source.
Another element is the atmospheric environment over the North Atlantic, which is often hostile due to high levels of vertical wind shear. This vertical wind shear is the change in wind speed and direction with height. It tears apart the vertical structure of a developing or mature tropical cyclone, preventing the storm from maintaining its organized, warm-core circulation.
Steering currents also play a significant role by dictating storm paths. Tropical storms initially move westward due to the trade winds, but eventually curve northward and eastward, following the mid-latitude westerlies and the jet stream. This path often directs them over colder waters or toward North America, causing them to weaken or transition. Consequently, most Atlantic hurricanes dissipate or transform long before crossing the 30th meridian west longitude.
When Atlantic Storms Impact Europe: Extratropical Transition and European Windstorms
When a tropical cyclone moves poleward, it undergoes Extratropical Transition (ET). During ET, the storm loses its warm-core structure and symmetrical shape, acquiring the frontal characteristics of a mid-latitude, cold-core system. The system is re-energized by the temperature contrast between the warm air it carries and colder air masses over the North Atlantic. This often intensifies it into a powerful extratropical low-pressure system, or a post-tropical cyclone.
These transitioned systems often merge with existing mid-latitude troughs or the jet stream, causing them to re-intensify dramatically as they approach Europe. Once they reach Europe, they are more accurately categorized as European Windstorms. While no longer hurricanes, these post-tropical cyclones can still be exceptionally destructive. Some of the highest-impact windstorms in Northern Europe are the result of ET.
The impacts on Europe from these post-tropical systems are primarily severe wind gusts, heavy rainfall, and coastal flooding. A notable example is the remnants of Hurricane Ophelia in 2017, which brought record-breaking gusts to Ireland and the United Kingdom. Similarly, the remnants of Hurricane Gonzalo in 2014 re-strengthened, impacting the United Kingdom and tracking across central Europe. Hurricane Lorenzo in 2019 affected the Azores before its extratropical remnants tracked toward the British Isles.