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Notice of Intent to Change the NCEP GFDL Hurricane Forecast System Brief description of change(s): Major upgrades to the GFDL Hurricane Prediction System have been made and tested for implementation for the ?03 hurricane Season. The most significant upgrades are the replacement of the deep convection and boundary layer physics with the physics from the GFS along with an increase in vertical levels. An improved initialization of the mass field is also being implemented in addition to an expansion of the ocean coupling and an initialization of the Gulf Stream. A list of all upgrades to the GFDL system can be found at: http://www.emc.ncep.noaa.gov/gfdl_2003_upgrades.pdf Reason for Change(s): GFDL physics has not been upgraded for many years, e.g. model deep convection was the moist convective adjustment scheme (Kurihara) The implementation of the GFS deep convection, e.g. SAS, along with an increased vertical resolution from 18 to 42 levels and the implementation of the GFS boundary layer will provide a more realistic interaction of the hurricane core circulation with the environment. These upgrades are important to improve overall track forecasts as well as improve intensity forecasts in highly sheared environments and scenarios conducive to intensification. Also, upgrades to the GFDL ocean model are being implemented to expand the model air-sea coupling and improve intensity (and track) forecasts in cases where SST?s changes are important. These upgrades are a part of a plan to improve the overall performance of the GFDL and to establish the GFDL as a benchmark in track performance in anticipation of transition to the Hurricane WRF (HWRF) system. The HWRF is expected to become operational in 2006. Schedule for change: Final testing completed [date]: March 2003 Expected implementation [date]: May 15, 2003 Description of testing: The upgrades were extensively tested for both the 2001 and 2002 hurricane seasons. The results of the reruns and testing can be found at: Statistical summaries [give Web site]: http://www.emc.ncep.noaa.gov/gfdl_2003_upgrades.pdf Forecast examples [give Web site]: http://www.emc.ncep.noaa.gov/gfdl_2003_upgrades.pdf Anticipated impact on forecasts: Improvements to both the track and intensity forecasts were anticipated with the upgraded GFS physics and increased vertical resolution. These upgrades are necessary to simulate the important role of the sub cloud layer in providing the deep convection with an improved vertical flux of heat and moisture. The improved representation of deep convection is essential to simulate and maintain the vertical structure of the hurricane through evolutionary stages of the interaction of the vortex with the environment. Summary of results: In 2001: track error was reduced ~15% for the 2-3 day forecasts in both the Atlantic and Pacific Basins. In 2002: improvements in the Atlantic track forecasts in the 3-5 day forecasts, ranged from 8% at day 3 to nearly 35% at 4-5 days. For both seasons: - elimination of the long standing northward bias was eliminated in EPAC forecasts along the Mexican coastline - skill for intensity forecasts was noted for particular case studies Further documentation available [give Web site]: http://www.emc.ncep.noaa.gov/gfdl_2003_upgrades.pdf Human point of contact for further information: Morris.Bender@xxxxxxxx Field Evaluation: Evaluation of all results were carried out by TPC hurricane specialists. Approvals: NCEP Director: L. Uccellini Date: March 31, 2003
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