Impact of New Global Models and Ensemble Prediction Systems on Consensus TC Track Forecasts

1. Impact of New Global Models and Ensemble Prediction Systems on Consensus TC Track Forecasts James S. Goerss NRL Monterey July 22, 2010

2. Background

3. Evolution of TC Track Forecast Error (nm) at NHC and JTWC NHC JTWC • NWP model improvements and the use of ensemble techniques have revolutionized TC track forecasting at NHC and JTWC. Today 5-day track forecast error is comparable to 3-day track forecast error in the 1990’s and 2-day track forecast error in the 1970’s.

4. Timeline for Operational Use of Global Models for TC Track Prediction 1992 – NOGAPS and UK Met Office global model at JTWC 1996 – Japanese global spectral model at JTWC 1998 – NOGAPS and UK Met Office global model at NHC; first consensus guidance at JTWC 2000 – NCEP GFS and first consensus guidance at NHC 2001 – NCEP GFS at JTWC (JTWC begins official 5-day forecasts) 2003 – NHC begins official 5-day forecasts 2005 – ECMWF global model at NHC 2006 – ECMWF global model at JTWC

5. Western North Pacific – Global Models 3-Year Weighted Mean 72-h Forecast Error (nm)

6. Atlantic – Global Models 3-Year Weighted Mean 72-h Forecast Error (nm)

7. Eastern North Pacific – Global Models 3-Year Weighted Mean 72-h Forecast Error (nm)

8. Background Summary Routine operational use of global model TC track forecasts began in the early 1990’s at JTWC and in the late 1990’s at NHC. The number of global models available has increased from 2 in the early 1990’s to the 4-5 that are available today, depending on the forecast center. Typical global model 72-h TC track forecast error has decreased from 300-400 nm in the early 1990’s to 150-200 nm today while typical 120-h error has decreased from 400-500 nm in the early 2000’s to 250-350 nm today. The increased number of models available coupled with model improvement has resulted in the reduction of consensus 72-h TC track forecast error from ~300 nm in the early 1990’s to ~150 nm today and the reduction of 120-h error from over 300 nm in the early 2000’s to just over 200 nm today.

9. NHC Track Forecast Guidance • Interpolated Model Guidance • AVNI – Global Forecast System (GFS) run at NCEP • GFDI – GFDL model run at NCEP • HWFI – Hurricane WRF run at NCEP • NGPI – Navy global model (NOGAPS) run at FNMOC • GFNI – GFDL model run at FNMOC • EGRI –UK Met Office global model • EMXI – ECMWF global model • TVCN – Consensus of above models (at least two) • CMCI – Canadian global model

10. Hurricane Alex

11. Initial Forecast Tracks Hurricane Alex - 18Z 25 June 2010

12. Forecast Tracks (24 h Later) Hurricane Alex - 18Z 26 June 2010

13. 2010 Hurricane Alex Non-Homogeneous TC Forecast Error (nm) 22 18 14 10 6 Number of Forecasts

14. 2009 Season

15. Atlantic 2009 Non-Homogeneous TC Forecast Error (nm) The Canadian Global Model performed very well. 86 55 42 30 18 Number of Forecasts

16. HFIP Demonstration • As part of the Hurricane Forecast Improvement Project Demonstration, a number of forecasts were made using different configurations of the NOAA/ESRL FIM (a global model using a flow-following vertical coordinate, finite-volume numerics, and an icosahedral global grid). Interpolated guidance was created from these model forecasts. • Interpolated Model Guidance • F8MI – FIM (30 km resolution, GFS initial conditions) • F8EI – FIM (30 km resolution, EnKF initial conditions) • F9MI – FIM (15 km resolution, GFS initial conditions) • F9EI – FIM (15 km resolution, EnKF initial conditions) • F0EI – FIM (10 km resolution, EnKF initial conditions)

17. Atlantic 2009 Homogeneous TC Forecast Error (nm) 56 41 34 24 16 Number of Forecasts

18. Atlantic 2009 Non-Homogeneous TC Forecast Error (nm) The 15-km FIM with GFS IC’s performed very well. 86 55 42 30 18 Number of Forecasts

19. Atlantic 2009 Homogeneous TC Forecast Error (nm) CON8 – consensus including CMCI and F9MI 82 55 42 30 18 Number of Forecasts

20. Eastern North Pacific 2009 Non-Homogeneous TC Forecast Error (nm) The Canadian Global Model was not a top performer. 203 131 79 47 24 Number of Forecasts

21. Eastern North Pacific 2009 Non-Homogeneous TC Forecast Error (nm) The 15-km FIM with EnKF IC’s was not a top performer. 203 131 79 47 24 Number of Forecasts

22. Western North Pacific 2009 Non-Homogeneous TC Forecast Error (nm) The 30-km FIM with GFS IC’s performed well. 502 404 311 236 179 Number of Forecasts

23. Western North Pacific 2009 Homogeneous TC Forecast Error (nm) CONX – consensus including F8MI 317 257 191 140 113 Number of Forecasts

24. HFIP Demonstration • As part of the Hurricane Forecast Improvement Project Demonstration, a 20-member ensemble was run using the 30-km FIM (EnKF IC’s) for a limited number of cases. Interpolated guidance was created from the ensemble mean of the member forecasts. • Interpolated Model Guidance • F8NI – Ensemble mean for 20-member FIM (30 km resolution, EnKF initial conditions) ensemble

25. Northern Hemisphere Homogeneous TC Forecast Error (nm) F8EI – FIM control F8NI – FIM ensemble mean 135 99 71 44 28 Number of Forecasts

26. Summary • Prior to the start of the 2009 Atlantic season, upgrades were made to the Canadian global model (CMCI) resulting in greatly improved TC track forecasts. • As part of the HFIP Demonstration a number of configurations of the FIM were run for the 2009 Atlantic season. It was found that the 15-km FIM using GFS initial conditions (F9MI) had the best TC track forecast performance. • A new consensus aid was formed by adding CMCI and F9MI to the TVCN models. For the Atlantic, the TC track forecast improvement for this new aid ranged from about 5 percent at 24 h to almost 10 percent at 120 h.

27. Summary • Neither the Canadian global model nor the FIM were among the top performers for the eastern North Pacific. Their addition to consensus did not result in significant impact. • The 30-km FIM using GFS initial conditions (F8MI) was run regularly for the western North Pacific and performed quite well. Its addition to the CONW consensus resulted in 5-10 percent track forecast improvement at 96 h and 120 h. • The track forecast improvement for the ensemble mean of the 30-km FIM using EnKF initial conditions EPS ranged from 10 percent at 24 h to over 15 percent at 120 h with respect to the control run. For a very limited sample, these ensemble mean forecasts were competitive with those from the multi-model consensus (TVCN/CONW).

28. Questions?

29. Atlantic – Global Models 3-Year Weighted Mean 120-h Forecast Error (nm)

30. Northern Hemisphere Homogeneous TC Forecast Error (nm) 136 88 65 47 29 Number of Forecasts

31. Atlantic 2009 Homogeneous TC Forecast Error (nm) 31 25 22 18 11 Number of Forecasts