27th-28th February 2010 Rapid Cyclogenesis Xynthia

During the days 27th-28th February 2010 Rapid Cyclogenesis Xynthia, coming from the Subtropical Atlantic Ocean with a deepening around 20 hPa/24 h and a minimum surface pressure of 968 hPa, crosses the Northwestern Iberian Peninsula and the Bay of Biscay into France. Although not as strong as other Cyclogenesis before (like Lothar in 1999, Klaus in 2009), it was very damaging:

65 deaths in several European countries; fundamentally in France, due to important coastal floodings caused by the spring high tide and a 1.5 meter storm surge, in Vendée and Charente-Maritime departments.
Property losses higher than 1000 million euros and around one million homes without electricity, specially in Western and Central France.

HRW v3.0 product (included in NWCSAF v2010) was run in the Iberian Peninsula & France National area (defined in the $SAFNWC/config directory as spain.cfg) during the days 27th and 28th February 2010, to show the possibilities of HRW product for the watch of this meteorological situation. Similarly to the December 2009 Cyclogenesis in Portugal, also available in this "NWCSAF Topical Images Section", and due to the large wind speeds that could be reached in this case, a larger difference than the default one has been permitted between the HRW wind components and the ECMWF wind guess used for their calculation, up to 144 km/h through configuration parameters LLAG_HRV = ELAG_HRV = 72; LLAG_IR = ELAG_IR = 24.

Filtering out the HRW output and considering only the strongest winds in the Very low layer (850-1000 hPa), defined in this case as 15 minute mean winds stronger than 89 km/h (Storm Force Winds), the areas to be considered in the meteorological watch and warning are clearly identified. In general, the HRW wind output shows::

The Very low level wind strength over France is more important than over the Iberian Peninsula.
Comparing with the December 2009 Cyclogenesis in Portugal, Hurricane force mean winds are much less widespread.
Sustained Storm Force Winds over land occur in France from the Western Coastal areas (Departments of Loire Atlantique, Vendée, Charente-Maritime and Gironde), into the Inner Country following a Northeastern trajectory.

Comparing HRW output in France (Storm force very low layer winds) with Surface winds observations (Maximum instant winds), the diagonal path followed by the strongest winds from the Charente-Maritime Department to the Ardennes is very similar in both figures.

Because of this, the capabilities of HRW product with its high density wind output for the watch and warning of areas affected by dangerous winds can be clearly seen.

Comparing against the ECMWF model wind fields, HRW v3.0 confirms the trajectory of Xynthia and the areas with strongest winds defined by the model, although winds are in general weaker than those expected by the model. In this case, the confirmation of the model by the HRW winds can also be useful for operative forecasting.

The high density wind ouput of HRW v3.0 and its temporal evolution permits also to know which regions can be suffering the hardest winds at every moment. This can also be very helpful for watch and warning tasks.