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

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

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

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

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. Participation of 1,614 local governments all over Japan highfairrelative lowlowno answer Satisfaction level Only 30% were highly satisfied. 65% demands more accuracy (smaller PC). 1 day 2 day 3 day 4 day 5 day Forecast from 1 to 5 October Analysis Survey of user satisfaction of 5-day track forecast - MELOR (0918) in October

Improvements of typhoon track forecast technicalcomponent presentation presentation component component Typhoon track forecast

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

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

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

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

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

1)Typhoon EPS operated experimentally since 2007 operated since 2008 Information on the distribution of forecast uncertainty Motivation of the introduction of new display form 2) 5-day track forecast operated experimentally since 2007 operated since km

NEPARTAK (0919) New display form

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

4-day5-day 4-day 5-day 4-day 5-day FT direction 10 deg. 130 deg. step.1 error relative to forecast track AFT error (km) CFT error (km) AFT error (km) CFT error (km) AFT error (km) CFT error (km) AFT error (km) CFT error (km) AFT error (km) CFT error (km) AFT error (km) CFT error (km) 332 cases 224 cases 108 cases 228 cases 84 cases 144 cases

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

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

Summary JMA has changed display form for typhoon track forecast with the improvements. 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. 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. JMA is considering the introduction of a new display form to track forecast in the next few years.

Thank you very much for your attention!

4-day 5-day 4-day 5-day circle radius: 440km circle radius: 510km circle radius: 650km circle radius: 550km hitting ratio (%) step2. comparison of performance between “circle” and “ellipse” with the same size 224 cases 108 cases84 cases 144 cases

We judge a forecast confidence level (A/B/C) by using the confidence information Typhoon EPS ensemble spread. What do we use for deciding a circle radius?ABC480km700km950km 70% PC radius is decided by using the conversion table from confidence level into the radius. as of 2009

TEPS Group AGroup B Group C 70% of cases of this Group are included within this position error (950km) The circle radius in each group is estimated based on the forecast verification result. How do we make the conversion table? as of 2009ABC480km700km950km 5-day circle radius