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NHC Track and Intensity Models Mark DeMaria NESDIS/CIRA RAMM Team COMET Presentation May 1999. Outline. TPC/NCEP Guidance Models Track, Intensity Forecast Procedure/ Products Forecast Examples Discussion. Factors Affecting TC Motion. Zero Order - Cons. of relative vorticity

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  1. NHC Track and Intensity Models Mark DeMaria NESDIS/CIRA RAMM Team COMET Presentation May 1999

  2. Outline • TPC/NCEP Guidance Models • Track, Intensity • Forecast Procedure/ Products • Forecast Examples • Discussion

  3. Factors Affecting TC Motion • Zero Order - Cons. of relative vorticity • Vortex Moves with “Steering Flow” • First Order - Cons. of absolute vorticity • Vortex induces beta-gyres and affects motion • General Model • Vertical structure is important • Interaction with orography, friction, convection

  4. Track Guidance Models • Zero Order - CLIPER, NHC90/91 • First Order - BAM, LBAR, VICBAR • General Models - GFDL, AVN, UKMET, NOGAPS, ETA

  5. CLIPER (CLIMatology and PERsistence) Statistical track model developed in 1972 Required Input: Current/12 h old speed/direction of motion Current latitude/longitude Julian Day, Storm maximum wind Avg. 24, 48, 72 h errors: 210, 450, 650 km Used as benchmark for other models

  6. NHC90 (Atlantic), NHC91 (East Pacific) • Statistical-Dynamical track model • Required Input • CLIPER forecast tracks • Deep layer mean heights (1000-100 mb) from NCEP global model forecast • New version for Atlantic with vortex removal scheme (NHC98)

  7. Typical Predictor Locations for NHC90

  8. BAM (Beta and Advection Model) • Follows trajectory in aviation run of MRF • Includes correction for “beta”-effect • Horizontal smoother (T25) applied to MRF wind fields • Three versions (BAMS, BAMM, BAMD) • Shallow: 850-700 mb • Medium: 850-400 mb • Deep: 850-200 mb

  9. LBAR (Limited-area BARotropic) • Shallow water equations on Mercator projection solved using sine transforms • Initialized with 850-200 mb average winds/heights from NCEP global model • Sum of idealized vortex and current motion vector added to large-scale analysis • Boundary conditions from global model

  10. GFDL Model • Sigma vertical coordinate (18 levels) • Finite difference model on lat/lon grid • 3 nested meshes (111, 37, 18 km) • Boundary layer, cumulus and radiation parameterizations • Large-scale analysis, boundary conditions from aviation run of MRF model • Sophisticated vortex initialization

  11. Outer Mesh of GFDL Model (Hurricane Georges 1998)

  12. Inner Mesh of GFDL Model (Hurricane Georges 1998)

  13. Total Wind Environment Vortex

  14. Vortex from global Analysis Vortex from spin-up procedure

  15. AVN 1000 mb Initial Wind/Vorticity 9/21/98 00 UTC (X indicates observed center of Hurricane Georges) X X

  16. 300 mb AVN Winds and WV Image 19 Sept 1998

  17. NOAA Gulfstream IV Jet

  18. 1998 Gulfstream IV Missions • 1 in July: Alex (1) • 7 in August Bonnie (4), Danielle (3) • 9 in September Earl (1), Georges (7), Hermine (1) • 2 in October Mitch (2) • 19 Total Missions

  19. Tropical Cyclone Intensity Change • Internal Control - evolution of the inner core • Thermodynamic Control - maximum intensity depends on SST and trop. temp. • External Control - inner core is modulated by environmental interactions

  20. Intensity Forecast Models • SHIFOR - Statistical, analogous to CLIPER • SHIPS - Statistical-Dynamical • GFDL - Primitive Equation • Inland Wind Decay - Parametric model

  21. SHIPS - Statistical Hurricane Intensity Prediction Scheme (Updated 1997) • Thermodynamic Predictors • SST potential (MPI-Vmax), 200 mb temp. • Synoptic Predictors • 850-200 mb shear, 200 mb zonal wind, 200 mb eddy momentum flux, 850 mb environmental vorticity, 200 mb divergence • Climatology and Persistence Predictors • Julian Day, Previous 12 h intensity change • SST evaluated along storm track, synoptic predictors from model forecast to 48 h

  22. Inland Wind Decay Model • Simple exponential decay function • Decay parameters fit to NHC best track intensities for U.S. landfalling storms • Developed from 1967-1993 storms • Separate algorithm for New England region (1938-1991 sample) • Forecast depends on initial intensity, speed of motion

  23. Improvements in Intensity Forecast Skill (Land Cases Excluded)

  24. Advisory Preparation Schedule (4 per day) • 00:00 Data collection, evaluate synoptic situation • 00:30 Satellite classification, recon fixes • 00:45 Prepare input, initiate guidance models • 01:15 Forecast preparation, NWS coordination • 02:00 NCEP/NWS/Navy coordination • 02:15 NAWAS, Caribbean coordination • 02:45 Complete and transmit advisory

  25. Overview of the Dvorak Technique • Visible and Infrared Technique • Uses patterns and measurements as seen on satellite imagery to assign a number (T number) representative of the cyclone’s strength. • The T number scale runs from 1 to 8 in increments of 0.5. • Additional rules determine current intensity

  26. Typical Examples of Patterns in Visible Dvorak Method Curved Band Ivan 1998 Shear Bertha 1996 Eye Georges 1998 Central Dense Overcast Georges 1998

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