Xynthia, a storm which caused many deaths and widespread disruption across Europe, particularly in France.
22 October 2020
26 February 2010
Most fatalities were the result of a powerful storm surge along the French west coast. Due to the combined effects of high tide and strong winds, the sea level rose up to 85 cm on 28 February 2010 at 0:00 off the Charente-Maritime and Vendée regions (source: CLS/Legos — AVISO).
by Javier García-Pereda (NWC SAF/AEMET )
During 27 and 28 February 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, crossed the Northwestern Iberian Peninsula and the Bay of Biscay into France.
Although not as strong as other cyclogenesis before (like Lothar in 1999 and Klaus in 2009), it was very damaging, causing:
- 65 deaths in several European countries. The worst was in the Vendée and Charente-Maritime departments of France, due to severe coastal floodings caused by the spring high tide and a 1.5 meter storm surge.
- Property losses higher than 1000 million euros and around one million homes without electricity, especially in Western and Central France.
Figure 1: Meteosat-9, 27 February 2010, 12:00 UTC
The Nowcasting SAF (Version 2010) software (High Resolution Winds (HRW) v3.0 product) has been run, in the Iberian Peninsula and French region for 27–28 February. This was done to show its possibilities for the watch and warning of dangerous strong wind situations.
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, as shown in Figure 2.
In general, HRW output shows:
- The Very low level wind strength over France is more important than over the Iberian Peninsula.
- Sustained storm force winds (shown in the figure as blue, yellow and red arrows) occur in France over land from western coastal areas (Departments of Loire Atlantique, Vendée, Charente-Maritime and Gironde), into the inner Country following a northeastern trajectory.
- Hurricane force winds (shown in the figure as red arrows) are much less widespread.
Figure 2: HRW v3.0 product, 27–28 Feb
Figure 3 shows the comparison between the HRW output over France ('Storm force very low level winds') with surface wind observations ('Maximum instant winds'). The diagonal path followed by the strongest winds from the Charente-Maritime Department into the Ardennes Department 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.
Figure 3: Comparison of HRW and observations
Figure 4 compares the HRW output against the ECMWF model wind fields. The HRW output 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 of HRW winds and their temporal evolution shows which regions can be suffering the most severe winds at every moment (this temporal evolution is shown by the different colours of HRW winds in the figure, related to different moments of the day). This can also be very helpful for forecasters needing to know when to issue warnings.
Figure 4: Comparison of HRW with ECMWF
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