Second IBTrACS Workshop, 11-13 April 2011, Honolulu, Hawaii

1

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

SummaryS.T. Chan

Hong Kong Observatory

11 April 2011

Second IBTrACS Workshop, 11-13 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, 11-13 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, 11-13 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 email)

Second IBTrACS Workshop, 11-13 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

JTWC CMA RSMC Tokyo

HKO

Averaging period (min)

1 2 10 10

Second IBTrACS Workshop, 11-13 April 2011, Honolulu, Hawaii

6

CI – MSW ConversionJTWC CMA JMA HKO

CI MSW (1-min, Dvorak, 1984)

MSW (Dvorak, 1984 - 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)

1.0 25 22 23

1.5 25 25 29 23

2.0 30 30 36 27

2.5 35 35 43 31

3.0 45 45 50 41

3.5 55 55 57 49

4.0 65 65 64 59

4.5 77 77 71 69

5.0 90 90 78 81

5.5 102 102 85 92

6.0 115 115 93 103

6.5 127 127 100 114

7.0 140 140 107 126

7.5 155 155 115 139

8.0 170 170 122 153

Second IBTrACS Workshop, 11-13 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, 11-13 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, 11-13 April 2011, Honolulu, Hawaii

9

Courtesy: Kishimoto/JMA

Second IBTrACS Workshop, 11-13 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)

JTWC CMA RSMC Tokyo

HKO

Best Track (provisional)

160 140 125 145

CI 7.5 7.5 8.0 7.5

Second IBTrACS Workshop, 11-13 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, 11-13 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, 11-13 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, 11-13 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, 11-13 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, 11-13 April 2011, Honolulu, Hawaii

16

Thank you