The Geophysical Fluid Dynamics Laboratory (GFDL) hurricane modelling system, initiated in the 1970s, has progressed from a research tool to an operational system over four decades. This system is still in use today in research and operations, and its evolution will be briefly described. This study used an idealized version of the 2014 GFDL model to test its sensitivity across a wide range of three environmental factors that are often identified as key factors in tropical cyclone (TC) evolution: SST, atmospheric stability (upper air thermal anomalies), and vertical wind shear (westerly through easterly). A wide range of minimum central pressure intensities resulted (905 to 980hPa). The results confirm that a scenario (e.g., global warming) in which the upper troposphere warms relative to the surface will have less TC intensification than one with a uniform warming with height. TC rainfall is also investigated for the SST-stability parameter space. Rainfall increases for combinations of SST increase and increasing stability similar to global warming scenarios, consistent with climate change TC downscaling studies with the GFDL. The forecast system's sensitivity to vertical shear was also investigated. The idealized model simulations showed weak disturbances dissipating under strong easterly and westerly shear of 10 m s^-1. A small bias for greater intensity under easterly sheared versus westerly sheared environments was found at lower values of SST. The impact of vertical shear on intensity was different when a strong vortex was used in the simulations. In this case, none of the initial disturbances weakened, and most intensified to some extent.

Robert (Bob) Tuleya received B.S. and M.S. degrees from the Pennsylvania State University. He retired in 2002 from NOAA's GFDL Laboratory after 31 years of federal service. While at GFDL, he worked in various positions in the Hurricane Dynamics Group, initially as a Research Associate and eventually became Group Head. He also served on internal committees, including the AMS Committee on Hurricanes and Tropical Meteorology and the USWRP research committee on Hurricane Landfall. As a NOAA visiting scientist, he has worked at CCPO in developing and upgrading the next generation Hurricane Weather and Research Forecast system (HWRF), which was implemented in 2007. Mr. Tuleya contintues to help maintain the GFDL forecast system, which is still being used as forecast guidance for the National Hurricane Center in the Atlantic and Eastern Pacific and by the U.S. Navy throughout the world. He continues to study the effect of global climate change on hurricane intensity and frequency with his colleagues at GFDL.

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