Evaluation and Development of Ensemble Prediction System for the Operational HWRF Model

1. Evaluation and Development of Ensemble Prediction System for the Operational HWRF Model Zhan Zhang, V. Tallapragada, R. Tuleya, Q. Liu, Y. Kwon, S. Trahan, J. O’Connor, and, W. M. Lapenta 65th Interdepartmental Hurricane Conference Miami, FL. Feb. 28 – Mar. 3

2. Outline Uncertainties in Hurricane Forecasts; Experiment Design; Results: - Track Forecasts - Intensity Forecasts Probabilistic Products; Summary & Future Works.

3. Possible Uncertainties in Hurricane Model Forecasts Initial Large Scale Flows; Lateral Boundary Conditions; Initial Storm Structure; Model Physics.

4. Experiment Design

5. List of Experiment: • Control: HWRF V3.2 Baseline, M21 • Large Scale Flow & LBC Perturbations: • - M00-M20, 21 members • - M27-M47, 21 members • Initial Storm Structure Perturbations: • - M23-M26, 4 members • Physics-Based Perturbations: • - M21, M22, M48, M49, 4 members • Total: 50 ensemble members • Hurricane Earl: 2010082512 -2010090412

6. Track Forecasts

7. More than ~15% improvement in track forecasts Track forecasts are improved by all sub-sets of ensembles; Ensembles have less impacts on the track forecasts before 48h;

8. GEFS-SAS GEFS-KF West bias at late stage Northeast bias Perturbed initial structure Physics-based Relatively narrow track spread

9. Intensity Forecasts

10. No clear intensity improvement from all sub-sets of ensembles. GEFS-SAS slightly better

11. Init intensity=35kts Init intensity=75kts Positive bias for weaker storm Negative bias for stronger storm For Earl, there are overall strong negative sample bias. Init intensity=50kts

12. Ranked Histogram for 10m Max Wind Speed Hurricane Earl, 2010 00h 24h 48h Relative Frequency (%) No sample bias at initial time 120h All time 72h Strong negative sample bias Ranked Ensemble members

13. Equal weights

14. ~ 17% Improvement Intensity forecasts are improved with weighted ensemble mean at all time levels

15. Hurricane Probabilistic Products

16. Ensemble Member-based Storm Strike Probability Forecast for 120h ens. mean Blue: obs Yellow: ens. mean obs.

17. Ensemble Spread (along/cross) Based Storm Strike Probability Forecast

18. Ensemble Intensity Forecasts

19. Probability Forecasts of 10m Wind Speed greater than 30m/s Earl, 2010082700 Max centers for wind speed and probability are not co-located Contour: Predicted 10m wind speed isotach from CTRL exp. Shading: Probability Forecast of 10m wind speed greater than 30m/s Double probability max centers

20. 120h Forecast of Strike Probabilities for Wind Speed greater than 20m/s, Earl, 2010082700 Danielle Earl

21. Summary & Future Works • Storm track forecasts are improved in all sub-sets of ensembles; • Model-based ensemble sample bias can be corrected by applying weights to ranked ensemble members; • Storm intensity forecasts are improved by weighted ensemble average; • HWRF is not very sensitive to storm initial radius of maximum wind; • Physics-based ensemble reduces model-based storm intensity bias; Future works: • Sensitivity test for storm initial positions; • Optimum combination of ensembles;

22. Storm Initial Position Uncertainties (All 2010 Storms)

23. Storm Initial Position PFD All 2010 Samples Gaussian–like distribution around zero ATL: lat EP: lat ATL:lon EP: lon