Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 1 ESCAP/WMO Typhoon Committee Best Track Consolidation Meeting, Dec 2010 Hong Kong Summary S.T. Chan Hong Kong Observatory 11 April 2011

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 2 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 The Meeting

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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. coastal radar & weather station observations from China; radar fixes from Taiwan to JTWC (via )

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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 JTWCCMARSMC TokyoHKO Averaging period (min) 1210

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 6 CI – MSW Conversion JTWCCMAJMAHKO CIMSW (1-min, Dvorak, 1984) MSW (Dvorak, adjustment from 10-min to 2- min subjectively determined) MSW (10-min, Koba et al., 1990) MSW (10-min, 0.9 of 1-min from Dvorak, 1984)

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 9 Courtesy: Kishimoto/JMA

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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) JTWCCMARSMC Tokyo HKO Best Track (provisional) CI

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 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

Second IBTrACS Workshop, April 2011, Honolulu, Hawaii 16 Thank you