1. TOPIC 3 CHAIR REPORT TROPICAL CYCLONE MOTION Russell L. Elsberry OUTLINE Need to improve track prediction –Importance of track forecast Opportunities to improve track prediction –Further improve model system –Optimum use of model guidance –Use of track ensemble –Better observations Guidance for discussion groups –Assistance required for forecast centers (T.C. Lee, Topic 3.1 Report) –Potential numerical model advances (S. Aberson, Topic 3.2 Report) –Opportunities for ensemble track prediction (S. Aberson, Topic 3.2 Report) –Opportunities for targeted observations (C. C. Wu, Topic 3.3 Report) IWTC-VI21-30 November 2006

2. NEED TO IMPROVE TRACK FORECASTS FIRST PRIORITY OF PARTICIPANTS AT INTERNATIONAL WORKSHOP ON TROPICAL CYCLONE LANDFALL RELATIVE CONTRIBUTIONS OF TRACK ERRORS, INTENSITY ERRORS, AND STRUCTURE ERRORS TO DeMARIA and KNAFF TRACK PROBABILITY DISTRIBUTIONS TRACK PERTURBATIONS ONLY IWTC-VI21-30 November 2006

3. TROPICAL CYCLONE MOTION SIZE PERTURBATIONS ONLY INTENSITY PERTURBATIONS ONLY IWTC-VI21-30 November 2006

4. TROPICAL CYCLONE MOTION OPPORTUNITIES TO IMPROVE TRACK PREDICTION FURTHER IMPROVE MODELS WESTERN NORTH PACIFIC 72-H TRACK FORECAST ERRORS DYNAMICAL MODEL TRACK ERROR TRENDS VERSUS CONSENSUS OF MODELS AND JOINT TYPHOON WARNING CENTER ERRORS JIM GOERSS PROVIDED COMPARISON OF REGIONAL MODELS COAMPS AND GFDN PLUS GLOBAL MODELS UKMO, GFS, AND NOGAPS JTWC BEGAN USING CONSENSUS OF FIVE MODELS DURING 2000. LATER NRL-MONTEREY ADDED FIVE MORE MODEL TRACKS FOR 72-H FORECASTS IWTC-VI21-30 November 2006

5. Western North Pacific (1992-2006) 72-h TC Track Forecast Error (nm)

6. TROPICAL CYCLONE MOTION PATHWAYS TO IMPROVE TRACK PREDICTION SINCE THE TEN-MEMBER CONSENSUS HAS PROVEN TO BE MORE SKILLFUL, ADDING MORE SKILLFUL MODEL TRACKS IS A VIABLE PATHWAY TO IMPROVED TRACK PREDICTION. SINCE GFS AND COAMPS HAVE NOT IMPROVED, AND THE SMALL IMPROVEMENT IN THE CONSENSUS DURING 2005 AND 2006 MAY BE ATTRIBUTED TO IMPROVED NOGAPS, GFDN, AND UKMO, SOME FURTHER IMPROVEMENT IN TRACK IS POSSIBLE FROM MODEL IMPROVEMENTS. JTWC ACHIEVED LARGE IMPROVEMENT FROM 1999 TO 2002 FROM ADOPTING CONSENSUS FORECASTING. ONLY IN 2004 WAS JTWC ABLE TO IMPROVE SLIGHTLY ON THEIR TEN-MEMBER CONSENSUS AT 72 H. IWTC-VI21-30 November 2006

7. TROPICAL CYCLONE MOTION IMPROVEMENT IN 120-H FORECASTS MAJOR ADVANCE SINCE IWTC-V HAS BEEN ISSUANCE OF 120-H TRACK FORECASTS THAT ARE AS ACCURATE AS 72-H FORECASTS LESS THAN A DECADE AGO. ONLY FOUR MODEL TRACK FORECASTS ARE AVAILABLE BEYOND 72 H. NOTE THAT JTWC DID NOT IMPROVE ON THE BEST MODEL OR THE CONSENSUS AT 120 H. IWTC-VI21-30 November 2006

8. TROPICAL CYCLONE MOTION OPTIMUM USE OF GUIDANCE - I DECREASING NUMBER OF SMALL SPREAD/LARGE ERROR (SSLE) CASES WILL REQUIRE BETTER MODEL 120-H TRACK GUIDANCE LARGE SPREAD/LARGE ERROR (LSLE) CASES HAVE COMPENSATING ERRORS THAT FORECASTER NEEDS TO RECOGNIZE IWTC-VI21-30 November 2006

9. TROPICAL CYCLONE MOTION OPTIMAL USE OF GUIDANCE - II POTENTIAL REDUCTION IN 120-H ERRORS FROM OPTIMUM USE OF GUIDANCE FOR 38 (33) LSLE CASES DURING 2004 (2005) SELECTIVE CONSENSUS (SCON) HAS POTENTIAL TO IMPROVE TRACK FORECASTING WHEN ONLY A SMALL NUMBER OF MODEL TRACKS ARE AVAILABLE AND ONE OR TWO TRACKS ARE CLEARLY ERRONEOUS IWTC-VI21-30 November 2006 SCON vsCONWSCON vsJTWC Year2004200520042005 Average239222203382 Maximum6266299321256 Minimum1364-8333

10. TROPICAL CYCLONE MOTION QUESTIONS FOR DISCUSSION GROUP FOR FORECASTING CENTERS What track guidance do all of the forecast/warning centers presently have available? [All centers represented at IWTC-VI should be queried] Is an improved track forecast a high priority for your forecast/warning center? Should all forecast/warning centers have access to a consensus of multiple skillful track forecasts? [Note Special Focus Session 3a] What would each forecast/warning center require to be able to have (and use) a skillful consensus track forecast? What should the WMO Regions and/or WMO-Geneva be doing to facilitate the availability of consensus track tools for those forecasting/warning centers that desire such a tool? Should the skill metric for track forecasting now be the consensus of available model tracks (rather than climatology and persistence)? IWTC-VI21-30 November 2006

11. TROPICAL CYCLONE MOTION QUESTIONS FOR DISCUSSION GROUP OPPORTUNITIES FOR IMPROVED MODEL SYSTEM What are potential numerical model advances? Higher horizontal and vertical resolution global and regional models –See Topic 3.2 report Physical process representations What are potential advancements in data assimilation that will lead to improved tracks? 4-D Variational vs. Ensemble approaches Incorporating environmental observations Incorporating vortex observations (if available) Are numerical models approaching the limit of track predictability? Should WMO prevail on all global model centers to provide track forecasts in all tropical cyclone basins? IWTC-VI21-30 November 2006

12. TROPICAL CYCLONE MOTION QUESTIONS FOR DISCUSSION GROUP OPPORTUNITIES FOR ENSEMBLE TRACK PREDICTION Does the tropical cyclone forecast center in your country produce, or have access to, an ensemble track prediction system? If yes, how are the ensemble track products used? If no, would they like to have such an ensemble track product? Is there a requirement (or a desire) in your country to issue probablistic track predictions (or a cone of uncertainty) about the line representing the forecast track? Is there a need for a training program in the use (by forecasters and customers) of ensemble track forecasts? Will the need for probablistic track forecasts provide more justification for adopting an ensemble data assimilation versus a variational approach? IWTC-VI21-30 November 2006

13. TROPICAL CYCLONE MOTION QUESTIONS FOR DISCUSSION GROUP OPPORTUNITIES FOR ENSEMBLE TRACK PREDICTION Should the IWTC-VI advocate that tropical cyclone tracks for each ensemble member from each participating country/activity be a standard product in The Interactive Grand Global Ensemble (TIGGE)? What research is necessary to make such a track ensemble into a useful product for forecasters? Note that initially the TIGGE is a research product that will only be available 48 hours after synoptic time and this limitation would have to be lifted for operational use. Would the availability of tropical cyclone tracks in all global tropical cyclone basins from all deterministic global models (e.g., Japan, China, Canada, France, Germany, Australia) in real-time be a useful product? IWTC-VI21-30 November 2006

14. TROPICAL CYCLONE MOTION QUESTIONS FOR DISCUSSION GROUPS OPORTUNITIES FOR TARGETED OBSERVATIONS What improvements in data assimilation and numerical models are necessary to obtain optimum benefit from targeted observations? Can one or more consortiums of countries be established to support expansion of aircraft targeting capabilities in various tropical cyclone basins? Can specific satellite soundings in sensitivity areas be extracted that would give similar improvements in track forecasts? What forecaster-relevant metrics should be used to evaluate the merit of targeted observations? What OSEs or OSSEs are required to optimize the targeted observations or the overall observational system? IWTC-VI21-30 November 2006