Tropical Storm Rolf


Tropical Storm Rolf, also known as Tropical Storm 01M and Invest 99L, was an unusual Mediterranean tropical storm that brought flooding to Italy, France, and Switzerland in November 2011, killing 12 people. Rolf originated from an extratropical system near western France on November 4. Despite the unfavorable conditions in the Mediterranean Sea, Rolf transitioned into a subtropical depression on November 7, before becoming a fully tropical storm later that day. On November 8, Rolf reached its peak intensity, with 1-minute sustained winds peaking at, and a minimum pressure of. During the next day, the storm made landfall on the island of Île du Levant, France, and soon afterwards, near Hyères in Southeastern France. Rolf quickly weakened and dissipated on November 10, following its second landfall. Rolf was the first tropical cyclone ever to be officially monitored by the NOAA in the Mediterranean Sea. Rolf was also the costliest Mediterranean tropical-like cyclone in the 2010s, with the storm causing at least $1.25 billion in damages.

Meteorological history

On November 4, an extratropical disturbance was spawned just off the coast of western France, within a cold front, by another extratropical cyclone to the north, named "Quinn." This storm began causing heavy rainfall in northern Italy, leading to flooding in the region. On the next day, a low-pressure area formed over western France, and the system was named Rolf by the Free University of Berlin, which names all significant low pressure systems affecting Europe. As the storm slowly moved eastward, it caused flooding in the Balearic Islands. Rolf gradually organized, and convection began to increase in the storm. Over the next couple of days, the storm continued to organize as it moved eastward, approaching the northwestern coast of Italy. On November 5, Rolf's forward motion slowed while the storm was stationed above the Massif Central in southern France, maintaining a central pressure of. On November 6, the system moved into the western Mediterranean Sea and stalled off the coast of Liguria, while gradually strengthening, bringing additional flooding to the region. Around the same time, the storm's frontal structure shrunk to in length. During that evening, Rolf spawned a tornado over Alassio, in northern Italy, causing some structural damage. On November 7, 2011, Rolf turned westward and slowly transitioned from an extratropical system into a subtropical depression over the warm waters of the Mediterranean Sea, with the system acquiring a warm quasi-symmetric core, and with organized convective rainbands wrapping around the center of the storm. The storm was then given the designation Invest 99L, by the United States Naval Research Laboratory. The NOAA also began watching the subtropical depression, which was now located in the Gulf of Lion. Later that day, Rolf transitioned from a subtropical depression into a tropical depression off the coast of France, and the NOAA gave Rolf the identifier 01M.
Late on November 7, Rolf attained tropical storm status as it completed its tropical transition, strengthening significantly in the process, with the NOAA noting that deep convention had persisted around the core of Rolf for long enough to officially declare the system a tropical storm. Consequently, both the Satellite Services Division and NESDIS of the NOAA classified the storm as Tropical Storm 01M. Rolf then began to bring heavy rainfall to the nearby countries in Western Europe, including Northern Italy and Eastern Spain. On November 8, Rolf strengthened further, as it approached the southeastern coast of France. On the same day, Rolf reached its peak intensity, with a minimum central pressure of, and maximum 1-minute sustained winds of. Rolf began to weaken on November 9, with the storm's convection decreasing and its upper- and mid-level circulation centers becoming misaligned. Later that day, Rolf weakened into a tropical depression shortly before making landfall in France, and the NOAA issued their final bulletin on the storm, as Rolf was expected to dissipate soon, with the storm weakening to around the time of its landfall. Later that day, Rolf made landfall on the island of Île du Levant, and soon afterward, made another landfall near Hyères, in Southeastern France, weakening rapidly upon making its second landfall. Early on November 10, Tropical Storm Rolf fully dissipated, following its second landfall.

Preparations and impact

Tropical Storm Rolf caused heavy flooding across Italy, France, and Switzerland, even as a precursor. From November 6-8, the storm dropped a total of of rain in about 72 hours over southwestern Europe. In both France and Italy, the heavy rainfall from the storm caused many rivers to overflow their banks, resulting in cities being flooded and enormous property losses ensuing. Officials in France noted that 16 departments in southern France sustained severe flooding and losses. Some of the hardest hit areas in France included Valleraugue, Sablières, Loubaresse, Draguignan, Arles, and Cannes, while in Italy, the cities that experienced the worst flooding were Genoa, Milan, Venice, and Turin. About 12 people total died from the storm; 6 people were Italian, and 5 were French. The storm caused at least $1.25 billion in damages, in the areas affected.
On December 16, 2011, the NOAA declared that they would no longer be monitoring storms in the Mediterranean Sea, possibly due to economic reasons and budget cuts. However, in 2015, the NOAA resumed services in the Mediterranean region, and by 2016, the NOAA was issuing advisories on a new tropical system, Tropical Storm 90M.

Italy

Prior to Rolf, northern Italy had already experienced a period of heavy rainfall during the first few days of November, which was later worsened by the additional rainfall brought by Rolf. The cities of Genoa and Recco in Liguria, in northern Italy, suffered some of the worst impacts from the storm, with Rolf's precursor bringing a period of prolonged rainfall since November 4. On November 4, Rolf killed 6 people and triggered the evacuations of a few thousand people in northern Italy, due to flooding from rainfall that began on the previous day. The Ferregiano, a leftward-flowing tributary of the Bisagno, overflowed its banks by. The Genoa-Sestri Levante section of Highway A12 in Italy was closed, due to the flooding, and air and rail traffic in the region were suspended. The road between Recco and Camogli was also flooded. On November 5, lightning struck the roof of a house in Camogli, starting a fire that was quickly put out by firefighters. The storm also caused multiple small landslides and downed numerous trees in Liguria.
Flooding from Rolf also led to traffic obstructions by November 6 in Piedmont and Tigullio, in the Province of Savona, after severe thunderstorms dumped large amounts of rainfall on the night of November 5–6. The flooding also caused blackouts in the Province of Savona on that night, and homes in the area suffered from flooded garages and basements. On the evening of November 6, Rolf spawned a tornado over Alassio, in the Province of Savona, damaging buildings and walkways in Piazza d'Italia, and flooding basements in the village of Barusso. In Calice al Cornoviglio, chasms opened up in the roads after multiple collapses, due to damage from the floodwaters. From November 6–7, of rain fell in Triora, in the Province of Imperia, which led to flooding in Sanremo that forced the evacuation of 25 families, with a total of 40 people, from a six-story building. On November 7, rainfall from Rolf caused a landslide in Savignone, which blocked Provincial Road 10. Rolf also caused a landslide in the Province of Genoa that broke the natural gas line between Casella and Montoggio, which was estimated to require 4 to 6 months to repair. In Genoa, schools closed from November 5–9. In total, Rolf caused at least $160 million in damages in Italy.
The Italian Government was criticized for the poor hydrogeological conditions in the city of Genova after Rolf, as well as the lack of safety measures for preventing the disaster, which led to a political controversy.

France

In southern France, 16 departments suffered severe flooding and damage from Rolf. The Department of Var in France was severely impacted by Rolf, with 2,500 people evacuated from the Argens region. The Alpes-Maritimes district along the Var River was also heavily impacted. During its landfalls, Rolf triggered floods across southern France, from the Pyrénées-Atlantiques all the way to the French–Italian border, as well as on the island of Corsica.
The Caisse Centrale de Réassurance, the French state insurance company, estimated that Rolf caused around €800 million in insured losses in France.