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Dynamic Hurricane Season Prediction Experiment with the NCEP CFS

Dynamic Hurricane Season Prediction Experiment with the NCEP CFS. Jae-Kyung E. Schemm January 21, 2009 COLA CTB Seminar Acknowledgements: Lindsey Long Suru Saha Shrinivas Moorthi. Outline. Description of the CFS experiment Datasets Used IRI Detection and Tracking Method

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Dynamic Hurricane Season Prediction Experiment with the NCEP CFS

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  1. Dynamic Hurricane Season Prediction Experiment with the NCEP CFS Jae-Kyung E. Schemm January 21, 2009 COLA CTB Seminar Acknowledgements: Lindsey Long Suru Saha Shrinivas Moorthi

  2. Outline • Description of the CFS experiment • Datasets Used • IRI Detection and Tracking Method • Analysis of storm activity statistics • Evaluation of CFS performance on environmental variables related to storm activity • A look at CFS-based predictions for 2008 season • Summary and future plan

  3. CFS T382 hurricane season experiments • One of the FY07/08 CTB internal projects • AGCM - 2007 operational NCEP GFS in T382/L64 resolution LSM - Noah LSM OGCM - GFDL MOM3 3. All runs initialized with NCEP/DOE R2 and NCEP GODAS. Initial conditions at 0Z, Apr. 19, 20, 21 and May 15(FY07) for 1981-2007. Forecasts extended to December 1. 4. For May 15 cases, runs in T62 and T126 resolutions also performed.

  4. Datasets • CFS hindcasts at T382 • May 15th Initial Condition • Output at every 3 hours • 1981-2007, 27 years • April 19th, 20th and 21st Initial Condition • Output at every 6 hours • 1981-2008, 28 years • More appropriate ICs for CPC Operational Hurricane Season Outlook • Observations from the HURDAT and JTWC Best Track Dataset • Tropical depressions and subtropical storms are not included in storm counts.

  5. Tropical Cyclone Detection Method • Based on method devised by Camargo and Zebiak (2002) at IRI • Detection algorithm uses basin-dependent threshold criteria for three variables • Vorticity, xthresh xthresh = 2sx • 10-m Wind Speed, uthresh uthresh = ugl + suugl= wind speed averaged over all global basins • Vertically integrated temp anomaly, Tthresh • Tthresh = sT/2 • Calculated using only warm-core systems

  6. Table of Basin Thresholds CFS T382 thresholds for vorticity, surface wind speed, and vertically integrated temperature anomaly for each ocean basin.

  7. Eight conditions must be met for a point to be considered a tropical cyclone 1. 850-hPa relative vorticity > xthresh 2. Maximum 10-m wind speed in a 7x7 box > uthresh 3. SLP is the minimum in the centered 7x7 box 4. Temp anomaly averaged over the 7x7 box and three pressure levels (300, 500, & 700 mb) > Tthresh 5. Temperature anomaly averaged over the 7x7 box is positive at all levels (300, 500, & 700 mb) * 6. Temperature anomaly averaged over the 7x7 box at 300mb > 850mb * 7. Wind speed averaged over the 7x7 box at 850mb > 300mb 8. The storm must last for at least 6 hours. * Criteria 5 & 6 define a warm core system.

  8. Storm Tracking • Once a point is designated as a tropical cyclone, the cyclone is tracked forward and backward in time to create a full storm track. • The maximum vorticity in a 5x5 grid around the cyclone is found and a new 3x3 box is formed around it. • At the next time step, if the maximum vorticity in this new box is greater than 3.5 x 10-5 s-1, the procedure is repeated. • This point has become part of the storm track. • If two storm tracks are the same, they are considered the same cyclone and counted as one.

  9. Four NH Ocean Basins

  10. Atlantic Eastern North Pacific Western North Pacific North Indian Examples of Storm Tracks for 4 NH Basins

  11. Atlantic Basin Atlantic Tropical Storms

  12. Eastern Pacific Basin Eastern Pacific Tropical Storms

  13. Western Pacific Basin Western Pacific Tropical Storms

  14. Atlantic Basin Correlations Anomalies of Atlantic Storms N=27 N=13 N=13 Red= Statistically Significant at 0.95

  15. ENP Correlations Anomalies of Eastern North Pacific Storms N=27 N=13 N=13 Red= Statistically Significant at 0.95

  16. WNP Correlations Anomalies of Western North Pacific Storms N=27 N=13 N=13 Red= Statistically Significant at 0.95

  17. Atlantic Basin ACE Index % of Normal N=27 N=13 N=13 Red= Statistically Significant at 0.95

  18. Correlations Total 81-93 94-06 IC=0419 0.24 0.19 0.01 IC=0420 0.34 0.32 0.40 IC=0421 0.25 0.38 0.24 April Ensm 0.35 0.16 0.34 IC=0515 0.22 -0.13 0.42 ATL Detrended Correlations N=27 N=13 N=13 Red= Statistically Significant at 0.95

  19. Correlations Total 81-93 94-06 IC=0419 0.46 0.23 0.15 IC=0420 0.38 0.36 0.45 IC=0421 0.29 0.25 0.10 April Ensm 0.49 0.22 0.30 IC=0515 0.35 0.11 0.49 ATL Detrended, Step Function Correlations N=27 N=13 N=13 Climatology used for detrending is broken into two 13-year periods, the inactive period of 1981-1993 and the active period 1994-2006 Red= Statistically Significant at 0.95

  20. Evaluation of SST and Wind Shear prediction for storm season

  21. JJA Nino 3.4 SST Index Red= Statistically Significant at 0.95

  22. ASO Nino 3.4 SST Index Red= Statistically Significant at 0.95

  23. JJA Atlantic MDR SST Index Red= Statistically Significant at 0.95

  24. ASO Atlantic MDR SST Index Red= Statistically Significant at 0.95

  25. JJA Atlantic MDR Shear Index Wind Shear: U200 – U850 Red= Statistically Significant at 0.95

  26. ASO Atlantic MDR Shear Index Wind Shear: U200 – U850 Red= Statistically Significant at 0.95

  27. TNA Non-Local Index, Jun-Nov [60W-30W; 5N-20N] - [0-360, 0-15N] SSTA Red= Statistically Significant at 0.95

  28. 2008 Atlantic Season Summary

  29. Atlantic Basin Prediction for 2008 • Two additional runs were made using July 15th and 16th initial conditions for 2008 only • Used as a trial run for the CPC Hurricane Outlook Update

  30. 2008 May Jun Jul Aug Sep Oct Nov Total 0419 1 1 5 3 2 1 1 14 0421 1 3 3 2 4 2 15 0422 1 3 3 3 1 11 ENSM 1 1.33 3.67 2.33 3 1 0.67 13.33 0715 2 4 3 9 0716 1 4 8 2 1 16 Obs 1 3 4 4 1 16 Atlantic BasinCFS 2008 Monthly Storm Count 3

  31. 2008 Atlantic Storm Tracks (Courtesy of Unisys) Large number of storms over the Gulf of Mexico this year

  32. Resemble Bertha and Cristobal

  33. .Summary • CFS in T382 resolution exhibits robust climatological seasonal cycle of tropical cyclone over four NH basins. • Warming trend and intensification of hurricane activity in the Atlantic basin captured in the CFS hindcasts. • Fair level of skill in predicting interannual variability of seasonal storm activities based on the limited number of forecast runs. • Model SST and wind shear bias explain part of less number of TCs in Atlantic and EN Pac. basins, in particular over the Gulf of Mexico. • Continue to increase number of ensemble members for better climatology and storm statistics. Hope to provide input for 2009 Hurricane Season Outlook with real time prediction runs. • Multi-model ensemble approach for dynamical hurricane season prediction is being explored.

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