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Storm surge forecast at Météo-France

Storm surge forecast at Météo-France. Pierre Daniel. Storm surge model. Two versions of one model: Overseas territories ( for tropical cyclones storm surges) Metropolitan coasts. Model installation. Model equations. Shallow water equations

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Storm surge forecast at Météo-France

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  1. Storm surge forecast at Météo-France Pierre Daniel

  2. Storm surge model • Two versions of one model: • Overseas territories (for tropical cyclones storm surges) • Metropolitan coasts

  3. Model installation

  4. Model equations • Shallow water equations • Finite differences on a fix grid mesh (Arakawa C) • At bottom: Chezy condition • Wind stress: Smith and Sandwell formulation • Coast: normal componant of current is set to zero • Open boundary: inverted barometer effect + radiation condition • Inputs: wind, atmospheric pressure, bathymetry

  5. Atmospheric forcing • Modified Holland model: pressure profile and gradient wind • Information needed: position, intensity, size • Provided by cyclone advisories • Example: • FORECAST VALID 21000Z 20.7S 165.8E. • MAX SUSTAINED WINDS OF 80 KT. • RADIUS OF 50 KT WINDS 65NE 40SE 25SW 40NW • RADIUS OF 34 KT WINDS 85NE 60SE 40SW 60NW

  6. Bathymetry • Hand extracted from nautical charts • 30 islands, grid mesh from 150 m to 2 km. • Examples:

  7. Model calibration • On selected cyclones from 1975 to 1990 • Very few tide gauges: 6 for 30 islands Largest surge: 250 cm in Guadeloupe (Hugo, 1989)

  8. Model forecasts • Largest surges: Luis, 1995 • estimated: 2 m in St Martin (2 m forecast) • measured: 40 cm in Guadeloupe (35 cm forecast)

  9. What is the best way to use the model ? Real-time forecast accuracy • When a hurricane is crossing an island, a small error in the trajectory forecast gives a large error in the space distribution of the surge. • Pre-computed storm surge data base • More than 1000 model runs for each island. • A data base available for graphical display on a computer.

  10. Storm surge data base

  11. Coastline of France • Same equations and numerical scheme • Wind stress: Wu formulation • Tide: 16 waves + 13 tide gauges • Calibration on selected situations (1987-1992) • In operation since October, 1999. • Under development: Improvement of the wind interpolation (spatial and temporal). • Sensitivity to atmospheric forcing: ECMWF, ARPEGE, ALADIN.

  12. Surges with ECMWF analyses (6 hours)

  13. Surges at La Rochelle (ECMWF analyses – 6 hours)

  14. Temporal frequency impact of atmospheric forcing at Le Verdon (ALADIN - December 27th, 1999)

  15. Next steps • Mediterranean sea • North sea • Wave surges in the lagoons • Real time access to tide gauge data • Data assimilation

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