Tropical cyclone wind radii estimation utilizing an empirical inland decay model John Kaplan (NOAA/HRD) Mark DeMaria (NOAA/NESDIS/ORA) Nicholas Carrasco (CIMAS/HRD) Jason Dunion (NOAA/HRD) 1. Introduction A revised version of the original Kaplan/DeMaria decay model (Kaplan and DeMaria 1995, 2001) that better handles tropical cyclones that traverse islands and peninsulas (DeMaria et al. 2006) was tested in real-time during the 2006 hurricane season as part of the NOAA Joint Hurricane Testbed (JHT). Implementation of the updated version of the model required significant modifications to the code that was employed to run the original version. Specifically, a wind field on a cylindrical grid with 5 km radial and 15 deg. azimuthal spacing was generated every hour along the NHC forecast track. The shape of the wind field was determined every hour by fitting the NHC official forecasted storm structure, intensity, and storm speed along the forecast track using a modified Rankine vortex. The wind field on the cylindrical grid was then decayed for time periods when the storm was over land using the updated version of the decay model. For time periods when the storm moved back over water, the trend in the official NHC intensity forecast was employed to adjust the decayed wind field. The resultant wind field was then sampled at desired time intervals to obtain estimates of the maximum wind and the radius of 34, 50, and 64 kt winds. 2. Results Since the updated decay model was not available for real-time testing until the middle of the 2006 hurricane season, the model was verified for an independent sample of landfalling Atlantic and E. Pacific basin hurricanes. Figure 1 shows the errors between the National Hurricane Center best track maximum wind and 64, 50 and 34 kt wind radii estimates and those from the decay model for the 11 hurricanes that made landfall in the Atlantic and E. Pacific basin during the period from 2004 -2006. For comparison, the errors between the NHC best track maximum wind and wind radii estimates and those from the GFDL, AVNO and NGPS models are also depicted. The errors were obtained by comparing the model and NHC best track estimates for initial (t=0 h) forecast times that were within 12 h of landfall. Errors were computed every 6 h until each system either dissipated or became extratropical. The figure shows that the maximum and wind radii estimates obtained using the new version of the decay model were generally in better agreement with the NHC best track estimates than both the old version of the decay model and the other numerical guidance for this sample. The lone exception was the 34 kt wind radii for which the AVNO model estimates were in better agreement. 3. References
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