Tropical Cyclone Prediction for HFIP with COAMPS-TC

1. Tropical Cyclone Prediction for HFIP with COAMPS-TC Richard M. Hodur1, S. Chen2, J. Cummings3, J. Doyle2, T. Holt2, H. Jin2, Y. Jin2, C.-S. Liou2, K. Sashegyi2, J. Schmidt2 1Science Applications International Corporation, Monterey, CA 2Naval Research Laboratory, Monterey, CA 3Naval 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. COAMPS Synthetics Synthetics to represent TC circulation NOGAPS First-Guess 900 km 900 km NOGAPS first-guess fields – have their own TC structure 900 km 900 km 0 20 40 Wind Speed (kts) COAMPS Analysis 900 km Improved TC representation with synthetics using 3DVAR 900 km High-Resolution Synthetic Observations for TC Initialization in COAMPS-TC Case: 0000 UTC 16 August 2009 (Bill; 03L) • 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) • 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

5. EPAC WATL 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

6. COAMPS-TC 2009 TC Forecasts WATL and EPAC

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

8. Issues with COAMPS-TC Forecasts for HFIP 2009 • 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

9. Bill Fred First several forecasts of Fred had a significant right bias First several forecasts of Bill had significant speed errors (too slow) 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 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.

10. 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 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. Other forecasts from the east Pacific and the west Pacific also exhibited a right bias, particularly in their early stages

11. 1. Track Error Related to Initial Intensity of TC WATL 2009 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

12. 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 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

13. Bill Results Fred Results Sensitivity Testing for Bill and Fred Effect of TC Vortex Specification and Lateral Boundary Conditions Smallest track errors with use of GFS and no synthetics Smallest track errors with use of NOGAPS and no synthetics 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

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

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

16. dBz dBz 48 h Radar Reflectivity 12 h Radar Reflectivity 2. Spotty Convection during Spin-Up of TC Bill: 2009081600 • 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. Initialization Physics Exchange Coefficients? Lack of Coupling? Mixing? . . . . ? Unbalanced Vortex 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

18. 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 12 h Intensity Change as a Function of Initial Intensity WATL 2009

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

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