INTERNATIONAL WORKSHOP ON SATELLITE ANALYSIS OF TROPICAL CYCLONES Honolulu, Hawaii, USA, 13 to 16 April 2011

RSMC Nadi Report

Introduction Satellite data has been the mainstay for tropical cyclone monitoring, detection, forecasting and warning services at RSMC Nadi ever since being designated a TC RSMC by WMO in 1985. The natural scarcity of terrestrial observational data in the South Pacific Ocean basin is largely responsible for this. Supplementary land-based surface observations particularly from radars and automated observing systems have significantly lifted the quality of detection and locating of tropical cyclone centres, but this comes with very high costs and limited spatial coverage. Lately, the availability of near real-time in- situ data, particularly scattterometer and microwave has given tropical cyclone forecasting operations the missing dimension. This needs to be supported for further research and development to enhance the timely provision of high impact forecasts which will subsequently lead to safety and security of lives and property in our most vulnerable communities.

Dvorak Technique Dvorak Technique has been the main tool for tropical cyclone intensity analysis at RSMC Nadi, to date. Training visitations from by Vernon Dvorak himself and proponents of the technique in the 1980’s helped set up RSMC Nadi operationalise this methodology, then.

Local Variations Dvorak Technique was developed for the North Pacific and Atlantic regions and adopting US wind averaging system as well as wind-pressure relationship. This has led to RSMC Honolulu always naming storms earlier than RSMC Nadi; has always been a contentious issue with our South Pacific communities. When used operationally in the South Pacific region, some minor adaptations had to be applied to normalize results.

Uniformity within Centres WMO and the Australian Bureau of Meteorology (BoM) have been instrumental in ensuring uniformity amongst TC forecasters in RAV through the biennial Southern Hemisphere TC training workshops in Australian Bureau of Meteorology Training Centre (BMTC) in Melbourne. Through the Pacific Public Sector Linkages Program Activity on Strengthening Regional Warning Services, where a BoM TC forecaster is seconded to RSMC Nadi, Nadi TC forecasters have been continually (every year) grounded in all aspects of Dvorak, thus enhancing uniformity amongst our analysts in this area.

Procedural Changes/Reviews In all, the initial Dvorak technique procedure has never been really changed since implementation in operational centres. It is probably the most stable of all meteorological techniques that has withstood time. However, in saying this, Nadi is working towards adopting some aspects of the technique that the BoM has revised and incorporated into their procedures. Nadi is going this way as this same procedure is being used in the biennial WMO Southern Hemisphere TC workshops in BMTC. Secondly, Nadi’s and Brisbane Best Track datasets of cyclones crossing our western border (160 East longitude) are now showing some glaring inconsistencies that must be addressed now. Technological advances The availability and creative use of complementary spectral information from today’s meteorological satellites affords the opportunity to advance the VIS/IR-based Dvorak technique. For example, polar-orbiting microwave sensors are being used to denote TC structure (Hawkins et al. 2001; Edson 2000) and to infer intensity (Herndon and Velden, 2004; Bankert and Tag, 2002). Employment of these instruments/methods in conjunction with the existing AODT into an integrated algorithm should provide analysts with a powerful consensus-type tool for estimating tropical cyclone intensity (Velden et al., 2004). Conceptual model of a satellite-based TC intensity analysis algorithm based on multispectral observations (Velden et al. 2004).

In addition, scatterometer data overlain atop microwave data can provide an effective supplement to enhance the Dvorak technique (right) during extra-tropical transition (Velden et al. 2004).Preliminary Results

At the final analysis, RSMC Nadi uses AODT dataAMS for comparisons before issuingSimple its N=268final intensities. AODT Bias 1.1 U 0.2 Avg0.7 0.5 ABS Error 7.4 4.6 4.7 4.2 RMSE 10.3 7.2 7.1 6.6

Estimates are for TC MSLP. All units in hPa. The Simple Avg is an average of AODT and AMSU. Weighted is a consensus of the 2 methods weighted by their individual errors. CI-pressure-wind relationship RSMC Nadi currently employs the John Knaff and Joe Courtney CI-pressure-wind relationship operationally as it is built into the TC Module application currently used by Nadi.

At the same time, Nadi still maintains the old Atkinson and Holliday wind-pressure relationship pasted below for best tracking purposes. TROPICAL CYCLONE CLASSIFICATION TABLE - RSMC NADI-TCC

10 Min Mean Wind Dvorak Pressure (hPa) 3 Sec Gust Estimated at 10 metres AGL Descriptive Severity CI Spin-Down Normal Small Terms Category Number km/h knots km/h knots Time (hrs) Cyclone Cyclone

2.0 999 999 45 25 65 35 18 - 24 2.5 997 997 55 30 85 45

995 995 65 35 95 50 Gale 1 3.0 990 990 75 40 100 55 1 987 987 85 45 110 60 DAMAGING 1 987 987 85 45 120 65 1 12 - 18 3.5 985 985 95 50 130 70 Storm 2 980 980 100 55 140 75 2 4.0 975 975 110 60 150 80 DESTRUCTIV 2 975 975 110 60 160 85 E 2

970 975 120 65 170 90 Hurricane 3 4.5 965 975 130 70 180 95 3 960 970 140 75 190 100 VERY 3 6 - 12 5.0 955 970 150 80 200 110 DESTRUCTIV 3 950 970 150 80 210 115 E 3 945 965 155 85 220 120 3

5.5 940 960 165 90 230 125 4 935 955 165 90 240 130 4 930 950 175 95 250 135 4 3 - 6 6.0 925 945 185 100 260 140 4 925 945 185 100 270 145 4 920 940 205 110 280 150 4

6.5 915 935 215 115 290 155 5 915 935 215 115 300 160 5 1 - 3 910 930 220 120 310 165 5 7.0 900 920 230 125 320 170 5

Best Track Criteria/Decisions In the data sparse area of the South Pacific, all observations are used for best tracking. No piece of data, available to TC forecasters, is ever discarded or ignored. All recorded data are quality checked and verified for relevancy and credibility before inclusion. In saying this, all RSMC Nadi has got in BT data is as shown below:

TC TOMAS ======NAME YYYY MM DD HHHH LAT LONG PRES W(KT) CAT ======Tropical Depression (TD) Phase

TOMAS 2010 03 10 0000 12.3 -172.2 1005 20 TOMAS 2010 03 10 0600 12.2 -172.3 1004 20 TOMAS 2010 03 10 1200 11.6 -172.9 1004 20 TOMAS 2010 03 10 1800 10.9 -173.3 1002 20 TOMAS 2010 03 11 0000 10.9 -174.0 1000 25 TOMAS 2010 03 11 0600 10.7 -174.5 1000 25 TOMAS 2010 03 11 1200 10.7 -175.1 998 30 TOMAS 2010 03 11 1800 10.6 -175.6 997 30

TC Phase Named by RSMC Nadi

TOMAS 2010 03 12 0000 10.6 -176.0 995 35 1 TOMAS 2010 03 12 0600 10.8 -176.4 990 40 1 TOMAS 2010 03 12 1200 11.1 -177.1 985 50 2 TOMAS 2010 03 12 1800 11.3 -178.0 985 50 2 TOMAS 2010 03 13 0000 11.7 -178.3 985 50 2 TOMAS 2010 03 13 0600 12.2 -178.6 980 55 2 TOMAS 2010 03 13 1200 12.5 -178.9 975 60 2 TOMAS 2010 03 13 1800 13.1 -179.0 970 65 3 TOMAS 2010 03 14 0000 13.5 -179.3 965 70 3 TOMAS 2010 03 14 0600 14.1 -179.4 950 80 3 TOMAS 2010 03 14 1200 14.6 -179.5 940 90 4 TOMAS 2010 03 14 1800 15.1 -179.5 925 100 4 TOMAS 2010 03 15 0000 15.6 -179.5 925 100 4 TOMAS 2010 03 15 0600 16.2 -179.6 925 100 4 TOMAS 2010 03 15 1200 16.6 -179.6 925 100 4 TOMAS 2010 03 15 1800 17.6 -179.5 940 90 4 TOMAS 2010 03 16 0000 18.6 -179.5 945 85 3 TOMAS 2010 03 16 0600 19.8 -179.2 950 80 3 TOMAS 2010 03 16 1200 21.1 -178.6 960 75 3 TOMAS 2010 03 16 1800 23.4 -177.8 965 70 3

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