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ESCAP/WMO Typhoon Committee Best Track Consolidation Meeting, 13-14 Dec 2010 Hong Kong Summary

ESCAP/WMO Typhoon Committee Best Track Consolidation Meeting, 13-14 Dec 2010 Hong Kong Summary. S.T. Chan Hong Kong Observatory 11 April 2011. The Meeting. Typhoon Committee – under joint auspices of UNESCAP & WMO, with focus on typhoons in the South China Sea & WN Pacific

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ESCAP/WMO Typhoon Committee Best Track Consolidation Meeting, 13-14 Dec 2010 Hong Kong Summary

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  1. ESCAP/WMO Typhoon Committee Best Track Consolidation Meeting, 13-14 Dec 2010 Hong KongSummary S.T. Chan Hong Kong Observatory 11 April 2011

  2. The Meeting • Typhoon Committee – under joint auspices of UNESCAP & WMO, with focus on typhoons in the South China Sea & WN Pacific • To discuss procedures / methodology used to locate a TC & determine intensity in real-time and during post-analysis review • To explore the feasibility of establishing a homogeneous & unified TC best track dataset • Attended by representatives from Shanghai Typhoon Institute (STI) of CMA, RSMC Tokyo, JTWC, HKO, WMO and Typhoon Committee Secretariat

  3. Deliberations at the Meeting • Presentations on methodology and procedures in use at different warning centres • Typhoon Megi (1013) used as case study to look for possible reasons for different maximum intensities estimated by different centres • The way forward & recommendations

  4. Major Findings • Each centre more or less uses the same observational data for TC analysis: satellite imageries, radar observations, surface station observations, QuikSCAT, ASCAT,… • But some centres receive additional data not available to others, e.g. coastalradar & weather station observations from China; radar fixes from Taiwan to JTWC (via email)

  5. Major Findings (Cont’d) • Dvorak a common & key analysis tool of all centres for TCs over the ocean • Yet, local rules adopted by each centre: • Wind-averaging period • Conversion from CI to maximum surface winds • Dvorak (1984) referred to by JTWC, CMA & HKO • Koba et al. (1990) by RSMC Tokyo

  6. CI – MSW Conversion

  7. Local adaption of Dvorak (Cont’d) • Landfalling TCs • JTWC stops conducting Dvorak for TC overland • RSMC Tokyo & HKO continue to perform Dvorak for landfalling TCs* At RSMC Tokyo, CI decreases with T-no. once TC makes landfall (i.e. Dvorak rule to hold CI for 12 hours not applied)* At HKO, weakening rule applied on a case-by-case basis

  8. Local adaption of Dvorak (Cont’d) • JTWC also refers to microwave imageries in determining TC intensity based on pattern matching • STI using two supplementary satellite analysis techniques based on cloud pattern (Dvorak-like) & TBB analysis (regression between intensity & convective cores attributes) – at post-analysis of TC only

  9. Courtesy: Kishimoto/JMA

  10. Case Study - T. Megi in 2010 • Dvorak analysis & best track intensity by different centres: • Highest MSW from Vortex messages during IOP-10 experiment: 165 kt (from SFMR)

  11. Case Study - T. Megi in 2010 (Cont’d) • Intensity estimates difficult to compare/verify: • Significant differences arising from different wind averaging periods & CI-MSW conversion • Vortex winds indicating gusts rather than typical wind field of TC? Courtesy: Kishimoto/JMA

  12. Case Study - T. Megi in 2010 (Cont’d) • Less discrepancy in CI from different centres-> CI a more reliable proxy of TC intensity • Study CI of historical TCs as a first step to develop a common best track dataset • Archive of CI available from JTWC & RSMC Tokyo • Archive from CMA available from 1985 onward

  13. Recommendations of Meeting • For the development of a common best track dataset, centres encouraged to exchange CI of historical TCs if available • Centres to make available to others the data used in determining TC location & intensity • Relay of Taiwan radar fixes by JTWC • Coastal radar & surface station obs. from CMA • Doppler radar wind information; WMO to consider expanding FFAA to include such information in the long term • HKO to issue satellite fixes via GTS; CMA also invited to do so

  14. Recommendations of Meeting (Cont’d) • Contacts of focal points of centres kept updated to facilitate exchange of information & data; TC web forum currently maintained by CMA be promoted • Centres to provide inputs on local adaptations/ rules/conversion tables used in Dvorak analysis-> HKO to set up forum online to facilitate the process-> Consolidated inputs to be incorporated in Typhoon Committee Operational Manual (TOM) by 2012 • JTWC to assist in clarifying use & interpretation of Vortex messages

  15. Follow-up on Vortex Messages • SFMR measures surface roughness (not winds) over 10-sec period • Algorithms developed to convert SFMR measurements to wind speed based on coincident dropsonde wind speed • NHC accepted SFMR data as TC MSW in US • Peter Black thinking of deriving a version of converting SFMR measurements to 10-min mean winds

  16. Thank you

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