Extreme Windstorm Xaver Poised to Batter Denmark and Germany

A developing extratropical low pressure system over the North Atlantic, dubbed "Xaver" by the Free University of Berlin, is predicted to "bomb" into a potent storm with winds near hurricane force that will bring damaging winds and storm tides to the coasts of Germany, the Netherlands, and Denmark on Thursday. By Thursday night, Xaver's center will cross southern Sweden, and damaging winds from the storm will sweep the coasts of Poland, Lithuania, and southern Sweden. The center of the low will pass over southern Norway, bringing strong northwest winds that will funnel down the North Sea. The European model predicts that at 18 UTC on Thursday, winds on the west coast of Denmark will be sustained near 58 mph (93 kph). Xaver will be accompanied by intense thunderstorms capable of mixing the stronger winds occurring aloft down to the surface, and wind damage may rival that of October's Extratropical Storm "Christian" (AKA the St. Jude storm), which bottomed out at 968 mb. Christian killed 18, and did $1.4 billion in damage. There is a smaller chance that the wind damage from Xaver will approach that of Windstorm Anatol, which hit Denmark, Southwest Sweden, and Northern Germany on December 3, 1999. Anatol had sustained winds of up to 91 mph (146 kph), killed 20 people, and injured over 800. Damage was $2.6 billion (1999 dollars) in Denmark, making it the costliest disaster in Danish history.


Figure 1. The European (ECMWF) model run performed at 12Z (7 am EST) on Tuesday, December 2, 2013, valid at 18Z (1 pm EST) Thursday, December 5, 2013, calls for winds in excess of 60 knots (69 mph) to affect the western coast of Denmark. The more recent 0Z Wednesday European model run has winds that are not quite as strong, about 5 mph less.

The predicted surface winds of Xaver will be similar to the ones the Netherlands experienced during the great February 1, 1953 North Sea storm that breached dikes in the Netherlands and England and killed over 2100 people. That storm bottomed out with a central pressure of 964 mb. Wednesday's 0Z European model run bottoms Xaver out at 964 mb, and the 12Z GFS is more intense, at 956 mb. However, the 1953 storm was much slower, and brought sustained winds in excess of 50 knots (57.5 mph) to the North Sea for more than 24 hours, allowing a huge storm surge in excess of 3 meters (10 feet) to pile up. In contrast, "Xaver" is expected to bring 50-knot winds to the North Sea for only about 9 hours, and the storm surge will not be as high as occurred in 1953. The maximum storm surge of Xaver will be in Germany and Denmark, farther to the east than occurred in the 1953 storm. The storm tide will be unusually high, since we are only two days past the new moon. Fortunately, the German coast is well protected by dikes, which are about 8 meters high, some even higher, and these dikes should be able to withstand Xaver's storm surge. The German weather service storm surge forecast made Wednesday morning called for a storm tide of 3 meters above average high tide in Cuxhaven, and 2.75 meters in Bremerhaven, during the high tide cycle early Friday morning.


Video 1. Winds from Windstorm "Christian" topple a tree that nearly kills a cyclist in the Netherlands on October 28, 2013.

German storm surge history
The deadliest flood of the last hundred years in Germany was the "North Sea flood" in 1962 (16/17 February), where many dikes broke and 340 people were killed. In the Bremerhaven area, the dikes from the 1840s were just able to withstand the storm surge but were heavily damaged. Bremerhaven had installed storm surge gates at the mouth of the river Geeste in summer 1961 as a reaction to the 1953 flood in the Netherlands. That small-scale Deltaworks saved the city. After this catastrophe, the dikes along the German coast were strengthened. Just in time, as the highest storm surge of at least the last hundred years occurred in January 1976. In Hamburg, the 1976 flood was 4.35 meters (14.3') above average high tide, which is 6.45 meters (21.2') above mean sea level. This is 75 cm higher than the storm surge of 1962, but the dikes were strong and high enough in 1976 to withstand the flood. Thanks go to Dr. Michael Theusner of the German climate museum Klimahaus for these stats.


Video 2. The great North Sea storm of February 1, 1953.

Links
24-hour storm surge forecasts and actual water levels for the North Sea coast
Tide chart for Bremerhaven, Germany. The highest storm tide will occur at high tide at 1:59 UTC (2:59 CET) on Friday morning.
German weather forum
Wikipedia's list of great European windstorms.
The Future of Intense Winter Storms, my 2010 blog post on climate change and winter storms (updated in early 2013.)

Jeff Masters