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Validation of 2008 Atlantic Storm Forecasts: Rainfall & Wind Structure Analysis

This workshop-focused study discusses the validation techniques for 2008 Atlantic storm forecasts, emphasizing rainfall patterns, volume, and extreme amounts, along with model wind structure evaluations. The importance of near-surface wind structure and clustering methods is highlighted. Skill indices, pattern matching assessments, and storm attributes are examined, addressing TC rainfall uniqueness. The comparative analysis indicates that GFS model demonstrates superior skillfulness in both 2005 and 2008 samples, despite varying resolutions among models. The study delves into storm Destructive Potential metrics, radial profiles, and wind distribution for a comprehensive verification approach.

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Validation of 2008 Atlantic Storm Forecasts: Rainfall & Wind Structure Analysis

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  1. Verification of model wind structure and rainfall forecasts for 2008 Atlantic storms HFIP Hurricane Diagnostics and Verification Workshop NHC, Miami, FL 04 May 2009 Tim Marchok NOAA / GFDL Collaborators: Rob Rogers (NOAA / AOML / HRD) Bob Tuleya (NCEP/EMC & Old Dominion Univ.) Mark Powell (NOAA / AOML / HRD)

  2. Motivation • Inland flooding from TC rainfall accounts for a significant percentage of deaths from U.S. landfalling TCs. • Storm size / structure has a major impact on the amount of damage at landfall. …both aspects have only recently begun to receive attention in terms of model evaluation

  3. Outline • Rainfall validation & techniques • Application of TC QPF validation techniques to 2008 U.S. landfalling storms • Development of model wind structure validation techniques • Application of wind structure validation techniques to 2008 Atlantic TCs

  4. Rainfall validation: What to focus on? • Rainfall patterns • Rainfall mean & volume • Extreme amounts

  5. The TC track: An anchor for QPF validation

  6. Example: Hurricane Gustav 72-h total rainfall HWRF GFDL Stage IV NAM GFS R-CLIPER

  7. 2008 Landfalling Storms

  8. Rainfall Patterns Equitable Threat Scores 2008 2005 Pattern Correlations: GFS (r = 0.78) HWRF (r = 0.60) GFDL (r = 0.53) NAM (r = 0.52) R-CLIPER (r = 0.51) (2008)

  9. Mean Rainfall

  10. Rainfall volume Comparison of rain volume bias by model 2005 2008

  11. 2008 Landfalling Storms 50% level Difference between obs rain value and fcst rain value at 50% level determines index

  12. Track-relative rain flux analyses

  13. Rain volume: Rain flux in select bands GFS, NAM GFDL, HWRF 0–100 km 300-400 km

  14. Skill Indices: Pattern Matching 2008 2005 • GFS performs the best in both samples • All models have skill relative to R-CLIPER

  15. Skill Indices: Mean / Volume 2008 2005

  16. Skill Indices: Extreme Amounts 2005 2008 • GFDL overforecasts the large amounts, HWRF underforecasts them, resulting in comparable indices • GFS performs best despite lowest resolution

  17. Rainfall Summary • Validation techniques address unique TC rainfall attributes: • Pattern matching • Rainfall volume • Extreme amounts • TC QPF skill indices for operational forecast evaluation • GFS most skillful in 2008 (similar to 2005)

  18. Outline • Rainfall validation & techniques • Application of TC QPF validation techniques to 2008 U.S. landfalling storms • Development of model wind structure validation techniques • Application of wind structure validation techniques to 2008 Atlantic TCs

  19. The importance of near-surface wind structure Area_TSKatrina = Factor of 9 Area_TSCharley

  20. Focus is on continuous / homogeneous methods • Distribution of Winds • Fractional areal coverage • PDFs of the winds • Radial Structure • Earth-relative profiles • Storm motion-relative profiles • Radius of max winds • Storm Destructive Potential • IKE, SDP, WDP (Powell and Reinhold 2007) • Others?

  21. Cases included in study…

  22. Distribution: Fractional Areal Coverage (34-kt winds) NW NE Storm- sample average at tau=00h SW SE

  23. Distribution: Fractional Areal Coverage (34-kt winds) NW NE Storm- sample average at tau=48h SW SE

  24. Distribution: Fractional Areal Coverage (64-kt winds) NW NE Storm- sample average at tau=00h SW SE

  25. Distribution: Fractional Areal Coverage (64-kt winds) NW NE Storm- sample average at tau=48h SW SE

  26. Radial profiles of the wind (all cases) NW NE Tau= 00h SW SE

  27. Radial profiles of the wind (all cases) NW NE Tau= 48h SW SE

  28. Radial profiles of the wind (Hurricanes only) NW NE Tau= 00h SW SE

  29. Radial profiles of the wind (Hurricanes only) NW NE Tau= 48h SW SE

  30. Radius of Maximum Winds

  31. Forecasts of Integrated Kinetic Energy GFDL Ike Intensity Forecasts HWRF Ike Intensity Forecasts Max Wind (kts) Max Wind (kts) GFDL Ike IKE (V>18 m/s) Forecasts HWRF Ike IKE (V>18 m/s) Forecasts IKE (TJ) IKE (TJ)

  32. Forecasts of Integrated Kinetic Energy

  33. Wind Structure Summary • Methods complementary to wind radii validation • Focus on various aspects of wind field • Distribution • Radial structure • IKE / Storm destructive potential • Others…? • Some biases already evident

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