1. Tropical Cyclone Prediction for HFIP with COAMPS-TC Richard M. Hodur 1, S. Chen 2, J. Cummings 3, J. Doyle 2, T. Holt 2, H. Jin 2, Y. Jin 2, C.-S. Liou 2, K. Sashegyi 2, J. Schmidt 2 1 Science Applications International Corporation, Monterey, CA 2 Naval Research Laboratory, Monterey, CA 3 Naval Research Laboratory, Stennis Space Center, MS Interdepartmental Hurricane Conference Savannah, GA 1-4 March 2010 HFIP: Hurricane Forecast Improvement Project

2. Tropical Cyclone Prediction for HFIP with COAMPS-TC Introduction COAMPS-TC performed well in TCS 2008 HFIP 2009 Goals: Run COAMPS-TC in real-time for west Atlantic and east Pacific TCs Assess the skill of the COAMPS-TC predictions Follow-on research to improve prediction of TC track, structure, and intensity Outline: COAMPS-TC Description Real-Time COAMPS-TC Runs during HFIP System configuration Discussion of Results/Implications Conclusion/Future Research

3. COAMPS-TC Coupled Ocean/Atmosphere Mesoscale Prediction System Analysis: Atmosphere: 3DVAR Analyses of u, v, T, and Heights (NAVDAS) Synthetic Observations Used to Incorporate TC Vortex (1000 – 400 mb) Relocation of TC in Background on Warm Starts Ocean: 2D OI of SST (NCODA) Model: Numerics: Nonhydrostatic, Scheme C, Sigma-z, Flexible Lateral BCs Parameterizations: PBL, Convection, Explicit Moist Physics, Radiation, Surface Layer TC Tools: Automated Moving Nests and Tracker, Dissipative Heating, Sea-Spray, Shallow Convection Features: Globally Relocatable (5 Map Projections) User-Defined Grid Resolutions, Dimensions, and Number of Nested/Parent Grids Incremental Data Assimilation Coupling to ocean and wave models not included in HFIP 2009 runs

4. Synthetic Observations Built From: Modified Rankine Vortex JTWC Warning Message w/Satellite Data NOGAPS T20/L15 truncated fields Blend Synthetics w/all other observations in 3DVAR (NAVDAS) Synthetics to represent TC circulation 900 km COAMPS Synthetics High-Resolution Synthetic Observations for TC Initialization in COAMPS-TC Case: 0000 UTC 16 August 2009 (Bill; 03L) Issues/Comments Some influence of NOGAPS TC circulation seen in COAMPS analysis fields (cold starts) For warm-starts, TC circulation is relocated to warning position Wind Speed (kts) 40200 NOGAPS first- guess fields – have their own TC structure NOGAPS First- Guess 900 km Improved TC representation with synthetics using 3DVAR COAMPS Analysis 900 km

5. Procedure for Running COAMPS-TC for HFIP 2009 45/15/5 km grids for WATL and EPAC basins 45 km grid fixed for all storms Inner 2 grids move with the TC All runs automatically submitted based on observed TC location/intensity at 0335 of each watch Forecasts run to 120 hours First run for each TC is a cold start, 12 h warm start for each subsequent run Output from each run posted on NRL web site; Forecast tracks sent to FSU and NCAR WATL EPAC

6. COAMPS-TC 2009 TC Forecasts WATL and EPAC

7. TC Track Forecast Errors in 2009 Homogeneous Samples West Atlantic Results East Pacific Results

8. 1.Track Error Related to Initial Intensity of TC Weakest storms (< 60 knots) exhibit the largest track errors at 12-24 hours; most often seen as a right-bias, but this can be a speed bias 2.Spotty Convection during Spin-Up of TC Model solutions exhibit spotty convection during first 24-30 hours until TC matures; Large impact on data assimilation 3.Initial Imbalance in TC Vortex for Strong TCs Predicted TC Intensity decreases in the first 6-12 hours when the initial maximum winds > 60 knots 4.Positive Bias in TC Intensity Forecasts There is a tendency in the model to make the TC too strong over the course of the 120 h forecasts Issues with COAMPS-TC Forecasts for HFIP 2009

9. Black line: Warning positions, large white circle with day at 0000 UTC, small white circle at 1200 UTC. Colored lines: COAMPS forecasts starting from different times with a circle every 12 hours. Bill First several forecasts of Bill had significant speed errors (too slow) Fred First several forecasts of Fred had a significant right bias 1. Track Error Related to Initial Intensity of TC Weakest storms (< 60 knots) exhibit the largest track errors; most often seen as a right-bias, but this can be a speed bias

10. Other forecasts from the east Pacific and the west Pacific also exhibited a right bias, particularly in their early stages Black line: Warning positions, large white circle with day at 0000 UTC, small white circle at 1200 UTC. Colored lines: COAMPS forecasts starting from different times with a circle every 12 hours. Felicia Guilliermo 1. Track Error Related to Initial Intensity of TC Weakest storms (< 60 knots) exhibit the largest track errors; most often seen as a right-bias, but this can be a speed bias

11. 12- and 24-hour track errors are worse when TC initial maximum wind speed is < 60 knots This has been found to occur in all basins 1. Track Error Related to Initial Intensity of TC WATL 2009

12. NOGAPS Synthetics: NOGAPS fields used for LBC, Synthetics used in NAVDAS to initialize TC Vortex structure (Benchmark) NOGAPS No Synthetics: NOGAPS used for LBC, TC Synthetics not used (only relocation of TC Vortex at initial time, no special DA of TC Vortex) GFS Synthetics: GFS fields used for LBC, Synthetics used in NAVDAS to initialize TC Vortex structure GFS No Synthetics: GFS used for LBC, TC Synthetics not used (only relocation of TC Vortex at initial time, no special DA of TC Vortex) NOGAPS: “early” run, 1-degree fields GFS: “real-time” run, ½-degree fields TC Vortex Specification and Lateral Boundary Condition Sensitivity Testing Hypothesis #1: Right-bias is largely caused by TC Vortex Specification (Synthetics) Hypothesis #2: Large-scale fields play a large role in TC motion

13. Sensitivity Testing for Bill and Fred Effect of TC Vortex Specification and Lateral Boundary Conditions Tracks are very sensitive to LBC (Ensembles?) and specification of the TC structure Track forecasts are improved (particularly, short-term) when synthetics are not used Bill Results Smallest track errors with use of GFS and no synthetics Fred Results Smallest track errors with use of NOGAPS and no synthetics

14. COAMPS-TC Forecast Tracks for TC Bill Effect of TC Initial Structure and LBC (Use of NOGAPS/GFS, Synthetics/No Synthetics) NOGAPS No Synthetics NOGAPS Synthetics GFS Synthetics GFS No Synthetics Largest Track Errors Smallest Track Errors

15. COAMPS-TC Forecast Tracks for TC Fred Effect of TC Initial Structure and LBC (Use of NOGAPS/GFS, Synthetics/No Synthetics) NOGAPS No Synthetics NOGAPS Synthetics GFS Synthetics GFS No Synthetics Largest Track Errors Smallest Track Errors

16. 2. Spotty Convection during Spin-Up of TC Bill: 2009081600 dBz 12 h Radar Reflectivity dBz 48 h Radar Reflectivity Model solutions exhibit spotty convection during first 24-30 hours until TC matures Can be very chaotic – not necessarily aligned in TC bands Most noticeable with weak storms Negatively influences first-guess fields for next analysis

17. 3. Initial Imbalance in TC Vortex for Strong TCs 4. Positive Bias in TC Intensity Forecasts WATL 2009 COAMPS-TC has tendency to weaken systems during first 12 hours, then strengthens them Initialization Unbalanced Vortex Physics Exchange Coefficients? Lack of Coupling? Mixing?.... ?

18. 12 h Intensity Change as a Function of Initial Intensity WATL 2009 Weak storms (<60 knots) tend to strengthen in first 12 hours of the forecast more than observed Strong storms (>60 knots) tend to weaken in first 12 hours of the forecast more than observed

19. SST Change (72 h) Air-Ocean Coupling in COAMPS-TC Predicts SST Cool Wake of 2-3°C Coupled Air-Sea Prediction of Bill with COAMPS-TC Microwave Satellite Derived SST Shows 2-3°C Cool Wake Similar to the Coupled Model COAMPS-TC air-sea coupled forecasts for Bill alleviate an over- intensification bias as a result of cool SST wakes Intensity Error (kts) 18-23 Aug Intensity Error Markedly Improved using Coupled Model Coupled Uncoupled

20. TC Prediction for HFIP 2009 with COAMPS-TC Conclusions/Future COAMPS-TC performed well in WPAC in 2008, 2009 (TCS) COAMPS-TC did not perform as well in WATL and EPAC in 2009 (HFIP) Problems with 2009 Performance related to: TC Vortex Specification: Largest Track Errors when Initial Intensity < 60 knots (Right Bias, Speed Bias) Significant Weakening of TCs > 60 knots in First 6-12 hours (Unbalanced TC Vortex) First few DA cycles of any TC suffers from spin-up (Spotty Convection) Positive Bias in Predicted TC Intensity (Physics? Coupling?.... ?) Follow-on Research: Eliminating the Use of Synthetics Suggests: Significant Improvement in Forecast Tracks (Positive Result) Reduction in the Weakening of Strong TCs in First 6-12 hours of forecast (Positive Result) Analyzed Intensity is Weaker than with Synthetics (Negative Result) LBC Sensitivity: Motivation for Ensembles using different Global LBC Future: DA, DA, DA, and Physics: Specification of TC Vortex in Analyses (Synthetics?, Model spin-up?, EnKF?, 4DVAR?, ?, ?, ?) Improved Handling of Convection on High-Resolution Grids (Initialization and Forecast) Improved Handling of Surface Fluxes (and all other Physical Processes) Air-Ocean-Wave Coupling (Recent Results are Encouraging) Interactions/Exchanges with HFIP, NOPP, and ITOP are Important Data Assimilation on cloud-resolving grids in a highly-convective environment is a formidable task