According to catastrophe modeling firm AIR Worldwide, Windstorm Andrea passed through the U.K. earlier this week, fast on the heels of Windstorm Ulli, which brought widespread travel and power disruptions to Scotland. Andrea- the first named European storm of 2012- formed southwest of Iceland on Tuesday, 3 January.
Late Wednesday (4 January), Andrea passed to the north of the U.K., bringing strong winds, particularly to central England, and causing power outages and travel disruption. “The system intensified as it traveled east. Early yesterday, Andrea was centered over Denmark with a central pressure of 964mb-down from 971mb the day before,” said Dr. Gerhard Zuba, senior principal scientist at AIR Worldwide.
In Germany today, the storm’s high winds have caused numerous roadway accidents, as well as power outages, and flooding. Indeed, Germany has been hardest hit by this early January storm, with flooding impacting the country’s northern region and high winds extending as far south as Bavaria. Western Austria, where Andrea’s heavy winds toppled trees that blocked roads and disrupted power, was also impacted.
When Andrea formed southwest of Iceland, it had hurricane-force winds. Forecasts at that time warned of a very strong wind event for the UK, the Netherlands, Denmark and Germany; appropriate warnings were issued by each of the national weather services. The Met office issued yellow warnings for rainfall levels.
According to AIR, Andrea’s path brought it north of Scotland and through the North Sea, then south to Denmark and Poland. Its strongest winds-to the south of the storm’s track-were ultimately weaker than expected. Thus, Andrea caused less disruption in the United Kingdom than had Ulli earlier in the week. Due to Andrea’s southeastward path, however, it went into Germany, which Ulli had bypassed; thus, Andrea had higher wind speeds in Germany than its predecessor.
Dr. Zuba continued, “Typically, strong extratropical cyclones approaching Germany from the North Sea, as Andrea did, push water against the German coast, causing flooding. Indeed, there was flooding in the low laying areas of Germany today (i.e., Hamburg). Also, because they obtain their energy from temperature gradients rather than from warm ocean water, which is the fuel for hurricanes, these storms can extend far inland. This explains why Andrea brought very strong wind gusts as far south as Bavaria today.”
Over the past few months, northern Europe has seen a number of significant storms pass through, beginning with Xaver and Yoda which impacted the region in late November. These were followed by Friedhelm in early December, both Joachim and Patrick (Dagmar) in late December, and Ulli (which formed on December 31st) in early January. This clustering effect of windstorms in Europe-storms following closely on the heels of one another-is a well-studied phenomenon and is explicitly accounted for in the AIR Extratropical Cyclone Model for Europe.
According to AIR, residential building stock in the areas affected by Andrea is predominantly of masonry construction. For commercial exposures, however, and particularly for commercial exposures in Germany, the building stock uses a wider variety of construction materials. Smaller office buildings, hotels, and other smaller commercial structures are usually masonry but larger buildings are generally made of reinforced concrete or steel.
According to AIR, little structural damage to these construction types is expected for wind speeds of the order widely experienced from Andrea, although damage to cladding, signage, and some isolated roof covering damage could occur. The flooding that occurred in Germany, however, may cause some damage; when residential buildings are subjected to floodwaters, most of the damage is limited to the basements, although the first floors of homes can also be submerged during severe flood events. In Germany, however, about 80% of all residential structures have basements, which alleviate the flood risk to floors above ground.
During Andrea’s passage over the United Kingdom, strong winds disrupted power to nearly 1,000 homes in Nottingham, 70 miles from the North Sea coast. Though Andrea impacted a region of the U.K. similar to that impacted by Ulli, its peak gusts were weaker, according to early meteorological observations from METAR stations in the UK. In Leeds and Bradford, England, peak gust recordings for Andrea were 120 km/h (about 75 mph). For Ulli, by contrast, the highest gust speeds were 170 km/h (106 mph), though these were recorded in Scotland.
Germany is suffering the brunt of Andrea today. In the north of the country, the storm brought high winds, rain, sleet, snow and storm surge. Munich, meanwhile, has experienced gusts up to 120 km/h (75 mph), as well as thunderstorms and heavy showers, according to the German Weather Service. The German Weather Service said the storm’s high winds were expected to continue until approximately 5pm local time today, after which the worst of the winds should cease, though hurricane-force gusts and heavy snow may still be possible at higher elevations.
Despite high winds, structural damage is expected to be limited from Andrea; there have been some reports of damage to roofs, but otherwise, traffic disruptions, uprooted trees and fallen branches are the major concern throughout the region.
High winds and snowfall should abate over the weekend. Andrea is forecast to continue moving eastwards, decreasing in strength, and taking a similar path to the path Ulli took earlier this week.
AIR continues to monitor the situation and will provide further updates as warranted