BOSTON, Dec. 6, 2013 – According to catastrophe modeling firm AIR Worldwide, Extratropical Cyclone Xaver has moved across Germany, the Netherlands, Denmark, and Poland. Wind speeds were recorded at 158 km/h when the storm reached Germany and heavy winds affected the Netherlands, Poland, and parts of Scandinavia. Massive storm surges have occurred along the coasts of southeastern England, the
Netherlands, and northern Germany.
“Xaver developed off the coast of Greenland on December 4, 2013 and its development was enhanced by another low-pressure system, Wilhelm, which was located over the Norwegian Sea on December 4-5,” said Dr. Nicolai Thum, senior research associate, AIR Worldwide. “Xaver passed north of Scotland on December 5, where its central pressure had dropped to 975 mb from a reading of 1010 mb less than 24 hours earlier. A pressure drop of this type, which deepens by 24 mb or more over 24 hours, often produces a phenomenon known as rapid cyclogenesis (or a weather “bomb”). Heavy winds were transported closer to ground level, bringing with them heavy precipitation and thunderstorms. By the morning of December 5, pressure levels had dropped 17 mb in three hours near Lerwick, Scotland, while it increased 18 mb over Sule Skerry. Later that day, over Thyboroen, Denmark, a pressure drop of over 14 mb in three hours was observed.”
Overnight, Xaver continued moving across the North Sea and reached northern Europe, packing strong winds, massive storm surges, rain, and snow. In Germany, wind gusts of up to 174 km/h were recorded at the North Sea island of Sylt, while sustained winds were 148 km/h. Wind speeds as high as 158 km/h struck Gluecksburg-Meierwik and reached as far inland as Brocken. Other recorded wind speeds include 148 km/h at the island of Spiekeroog, 144 km/h at Fichtelberg and Leuchtturm Kiel, 140 km/h at Strucklahnugshoern (Nordsee), and 137 km/h at Rostock, Warnemuende, and Buesum. Northern Poland received wind speeds as high as 160 km/h, while similar gusts were reported in parts of the Czech Republic.
Dr. Thum continued, “The greatest threat from Xaver has been the high spring tides, which along with Xaver’s slow track have enhanced storm surges on Thursday and Friday. The storm surge in the United Kingdom and the Netherlands is the highest seen since the deadly North Sea floods of 1953; however, disaster has been averted thanks to strengthened flood defenses in both countries.”
In England, the Thames Barrier will be closed for the second time in two days in accordance with the tide, preventing the surge from reaching London as it did in 1953. Xaver’s surge caused a difference of two meters in water height between the front and back of the barrier.
Flood defenses in the Netherlands successfully held back the rising water by closing off the Eastern Scheldt barrier for the first time since 2007. In southwestern Zeeland, the sea reached 3.99 m above mean sea level. Germany is comparing Xaver to the 1962 floods, which submerged nearly a fifth of Hamburg’s municipal area with water 5.7m above mean sea level. Xaver’s storm surge reached 4-6m above mean sea level. However, the area has fared far better thanks to Germany’s 8m dikes.
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The storm is slow moving and the relentless battering from winds can weaken structures, increasing their vulnerability. A sea cliff in Hemsby, England, collapsed on Friday, causing several homes to tumble into the sea. Extreme flooding was seen along several communities in southeastern England including Whitby, where about 100 homes received over a meter of water. Lowestoft, Whitby, Great Yarmouth,
and Saltburn also experienced flooding. Storm surges along western Great Britain affected several cities including Blackpool. Flood defenses failed at the English cities of Lincolnshire and Boston.
Roof damage is widespread and fallen trees have damaged homes and autos. Railways, roads, and bridges have been closed due to strong winds, high water and debris.
According to AIR, most of the residential buildings in the United Kingdom are detached, semi-detached, or terraced (row) houses and are primarily of masonry construction. Single-family homes in Germany, Denmark, the Netherlands, and Poland, are also predominantly of masonry construction, although a small percentage are wood frame, and are mostly low-rise. Sweden’s building stock has a much higher percentage of wood frame buildings. Mid-rise residential buildings generally have exterior non-load bearing walls made of masonry although they may have light-gauge steel stud walls or concrete panels. Under high winds, most of the damage in built up areas is to rooftops and chimneys of residences, although walls are often damaged by flying debris.
Floods can affect a significant portion of low- and mid-rise buildings, particularly the cellars. Risk is particularly high for finished cellars with furniture and appliances; some may contain entire apartments. Usually, heavily used cellars have better flood defense mechanisms than unfinished ones. Large apartment and condominium buildings often have a higher level of engineering and are more resistant to wind damage. Wind damage ratios for tall buildings are lower because the roofs are a smaller portion of the building as a whole. However, balconies, awnings, and sliding glass doors are susceptible to wind damage.
According to AIR, commercial exposures use a wider variety of construction types. Smaller buildings are usually masonry and perform similarly to residential buildings under strong winds. Larger buildings are generally reinforced concrete or steel, and wind damage is typically to nonstructural components such as mechanical equipment, roofing, cladding, and windows. Large commercial buildings often have a large amount of external glass, which is quite vulnerable to wind damage. Flood vulnerability is usually mitigated by flood defenses, although lower floors and cellars often contain services, fixtures, and electrical and mechanical fittings.
As of 15:00 GMT, December 6, 2013, Xaver is stationary over the Baltic Sea and winds are still impacting a wide region. The winds are dissipating and the storm is expected to end later today. AIR is monitoring this storm closely and will provide updated information next week.