Portugal is far from the tropical breeding grounds of the Atlantic, making true hurricane landfalls extremely rare. However, the threat of severe weather from the Atlantic is real. The region is regularly affected by powerful systems that bring destructive winds and torrential rain. These events are often systems that have transitioned out of their tropical phase but still retain substantial strength as they cross the ocean toward Europe.
Defining the Tropical Cyclone Threat
A tropical cyclone, known as a hurricane in the Atlantic basin, is a low-pressure system characterized by a warm core and a closed, organized circulation. These systems draw immense energy from the heat released when water vapor evaporates and condenses into rain clouds. For a tropical cyclone to form and intensify, sea surface temperatures (SSTs) must consistently be \(26.5^\circ\text{C}\) or higher, extending to a significant depth. This warm water is the primary fuel source for the storm’s engine.
The system is classified based on its wind speed and core structure. A tropical storm becomes a hurricane when sustained winds reach \(119\text{ km/h}\). A subtropical storm shares characteristics of both tropical and extratropical storms, often featuring a less symmetric wind field.
The Atlantic’s Natural Defenses
Portugal’s geographic location provides substantial natural protection against the most powerful tropical systems. The primary defense is the generally cool temperature of the eastern North Atlantic Ocean. The minimum \(26.5^\circ\text{C}\) threshold required to sustain a hurricane is rarely met near the Iberian Peninsula. This lack of warm water causes the storm to weaken or begin a transformation process long before it reaches the Portuguese coast.
The typical steering currents for Atlantic hurricanes tend to carry them westward or northwestward, away from Europe. The large, persistent high-pressure system known as the Azores High often acts as a meteorological barrier, deflecting storms further north into the open ocean. Only when this high-pressure system is weaker or positioned unusually far to the west does a storm have a clear path toward the Iberian coast.
The Real Severe Weather: Post-Tropical and Extratropical Systems
The most common severe weather threat to Portugal comes from systems that have undergone extratropical transition (ET). This occurs when a tropical cyclone moves over colder water and interacts with the mid-latitude jet stream and weather fronts. The storm loses its warm core and centralized energy source, transforming into a cold-core, extratropical cyclone, sometimes referred to as a European windstorm. Unlike their tropical counterparts, these extratropical systems gain their energy from the temperature contrast between different air masses.
Despite the change in classification, these post-tropical cyclones can still be powerful, retaining high wind speeds and carrying significant moisture. Portugal frequently experiences the effects of these systems, which produce widespread heavy rainfall, strong gusts of wind, and coastal flooding. The transformed storm often develops a much wider wind field, affecting a larger area of the country than a compact hurricane would.
Historical Impacts on the Iberian Peninsula
While true hurricane landfalls are exceptionally rare, Portugal has been affected by tropical and post-tropical systems several times in modern history. Hurricane Vince in 2005 was a remarkable exception, forming unusually far east in the Atlantic before weakening to a tropical depression and making landfall in Spain, bringing rain to parts of Portugal. In 2020, Subtropical Storm Alpha made landfall in northern Portugal at peak intensity, marking a rare event of a named storm hitting the mainland.
The most potent recent example was Post-Tropical Cyclone Leslie in 2018, which made landfall near Figueira da Foz. Leslie was still a Category 1 hurricane just hours before reaching the Portuguese coast. Though it transitioned into a post-tropical cyclone, it brought wind gusts exceeding \(175\text{ km/h}\) to some areas. Leslie caused extensive damage and widespread power outages across central Portugal.