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Improvement of the JMA typhoon track forecast

Improvement of the JMA typhoon track forecast. Kenji KISHIMOTO National Typhoon Center Forecast Division JMA. 1. Objective of track forecast. 2. JMA display form for track forecast. 3. Future challenge.

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Improvement of the JMA typhoon track forecast

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  1. Improvement of the JMA typhoon track forecast Kenji KISHIMOTO National Typhoon Center Forecast Division JMA

  2. 1. Objective of track forecast 2. JMA display form for track forecast 3. Future challenge

  3. 1. Objective of track forecast 2. JMA display form for track forecast 3. Future challenge

  4. Various disasters caused by typhoons flood high wave landslide strong wind storm surge Disaster-prevention activities are carried out based on typhoon track forecasts.

  5. I should prepare for the typhoon. A forecasted track shown as area that covers forecast uncertainty (Probability Circle: PC)

  6. Survey of user satisfaction of 5-day track forecast - MELOR (0918) in October 2009 - Participation of 1,614 local governments all over Japan Analysis Forecast from 1 to 5 October Only 30% were highly satisfied. 65% demands more accuracy (smaller PC). 1 day 2 day 3 day 4 day 5 day high fair relative low low no answer Satisfaction level Provider (Met. Service) wants to show a PC as big as possible when forecast is difficult. User (government, etc.) wants to see a PC as small as possible in view of saving costs of disaster preparation activities.

  7. Improvements of typhoon track forecast Typhoon track forecast presentation component technical component

  8. 1. Objective of track forecast 2. JMA display form for track forecast 3. Future challenge

  9. Present display form of JMA track forecast 4 times/day (00, 06, 12, 18 UTC) 3-day track & intensity forecast If it is expected to hold TS intensity or higher in the next 3 days, then 5-day track forecast issued in 90 minutes issued in 50 minutes Day 5 70% probability circle (PC): the range into which the center of a TC is expected to move with 70% probability at each validation time. Day 4 Over-50kt-wind area (analysis) 70% PC Day 3 Over-30kt-wind area (analysis) Storm warning area: 70 % PC + forecasted area of 0ver-50kt-wind

  10. Track of track forecast errors (annual & 5-year mean) 3 day 2 day km 1 day year

  11. History of display form (Start of TV service) 1982 1953 1986 1997 2004 Present 8 circular form + strong wind area sectorial form circular form Display form PC + over-50kt-wind area 60% PC to 70% PC in 1997 PC reduction by 10% in 2004 by 15% in 2008 directional accuracy + speed accuracy 60% PC Only directional accuracy Needs to be improved no display of TC movement speed accuracy misunderstanding of PC center as TC center and PC as strong wind area

  12. 1. Objective of track forecast 2. JMA display form for track forecast 3. Future challenge

  13. Motivation of the introduction of new display form • Typhoon EPSoperated experimentally since 2007 operated since 2008 Information on the distribution of forecast uncertainty 2) 5-day track forecastoperated experimentally since 2007 operated since 2009 950km

  14. NEPARTAK (0919) New display form

  15. Provisional forecast verification (Jul. 2007 - Oct. 2009) step.1 error relative to forecast track 5-day vertical axis: along FT (AFT) AFT error error 4-day CFT error horizontal axis: cross FT (CFT) 3-day analysis track forecast track (FT)

  16. step.1 error relative to forecast track 10 deg. 4-day 5-day FT direction 332 cases 228 cases AFT error (km) AFT error (km) 130 deg. CFT error (km) CFT error (km) 4-day 5-day 5-day 4-day 224 cases 144 cases 108 cases 84 cases AFT error (km) AFT error (km) AFT error (km) AFT error (km) CFT error (km) CFT error (km) CFT error (km) CFT error (km)

  17. step2. comparison of performance between “circle” and “ellipse” with the same size 4-day, FT direction: 10-130 deg. Hitting ratio (%) 729km (510/0.7km) 70% 72% 357km (510x0.7km) 510km AFT error (km) 729km (510/0.7km) 357km (510x0.7km) 108 cases 56% CFT error (km)

  18. Idea of makig “probability ellipse” Step 1. deciding centers of a circle Step 2. making a basic circle based on ensemble spread Step 3. deforming a basic circle within a fixed range to make an ellipse using the distribution of Typhoon EPS members 4-day, FT direction: 10-130 deg.

  19. Summary • JMA has changed display form for typhoon track forecast with the improvements. • Typhoon EPS, operated since 2008, provides the information on the distribution of forecast uncertainty. • JMA is considering the introduction of a new display form to track forecast in the next few years.

  20. Thank you very much for your attention!

  21. step2. comparison of performance between “circle” and “ellipse” with the same size 4-day 5-day 5-day 4-day 224 cases 144 cases 108 cases 84 cases hitting ratio (%) hitting ratio (%) hitting ratio (%) hitting ratio (%) circle radius: 440km circle radius: 550km circle radius: 510km circle radius: 650km

  22. What do we use for deciding a circle radius? • We judge a forecast confidence level (A/B/C) by using theconfidence information Typhoon EPS ensemble spread. • 70% PC radius is decided by using the conversion table from confidence level into the radius. as of 2009

  23. How do we make the conversion table? • The circle radius in each group is estimated based on the forecast verification result. Group C Group A Group B 70% of cases of this Group are included within this position error (950km) TEPS 5-day circle radius as of 2009

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