Storm%20surge%20forecast%20at%20M

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Storm surge forecast at Météo-France
Pierre Daniel
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Storm surge model

• Two versions of one model
• Overseas territories (for tropical cyclones storm
  surges)
• Metropolitan coasts

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Model installation
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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

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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

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Bathymetry

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

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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)
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Model forecasts

• Largest surges Luis, 1995
• estimated 2 m in St Martin (2 m forecast)

• measured 40 cm in Guadeloupe (35 cm forecast)

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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.

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Storm surge data base
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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.

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Surges with ECMWF analyses (6 hours)
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Surges at La Rochelle (ECMWF analyses 6 hours)
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Temporal frequency impact of atmospheric forcing
at Le Verdon (ALADIN - December 27th, 1999)
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Next steps

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