Numerical Simulations of the Genesis of Hurricane Diana (1984). Part II: Sensitivity of Track and Intensity Prediction

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Abstract
The authors examine numerous simulations that probe the dynamics governing the intensification and track of Tropical Cyclone Diana (1984) simulated in Part I. The development process is fundamentally dependent on a preexisting upper-tropospheric trough–ridge couplet. This couplet focuses mesoscale vertical motion that, in turn, produces lower-tropospheric potential vorticity (PV) anomalies, which form the seed for the tropical storm. Removal of this trough–ridge couplet from the initial conditions eliminates cyclogenesis. The simulated rate of development of Diana in the prehurricane phase depends principally on choices of cumulus parameterization, boundary layer treatment, sea surface temperature, and grid spacing. Simulations with cumulus schemes that allow more grid-scale precipitation on the 9-km grid exhibit unrealistic grid-scale overturning and slower intensification, primarily due to production of cyclonic vorticity anomalies at large radii. Use of an innermost nest with 3-km grid spacing... Abstract The authors examine numerous simulations that probe the dynamics governing the intensification and track of Tropical Cyclone Diana (1984) simulated in Part I. The development process is fundamentally dependent on a preexisting upper-tropospheric trough–ridge couplet. This couplet focuses mesoscale vertical motion that, in turn, produces lower-tropospheric potential vorticity (PV) anomalies, which form the seed for the tropical storm. Removal of this trough–ridge couplet from the initial conditions eliminates cyclogenesis. The simulated rate of development of Diana in the prehurricane phase depends principally on choices of cumulus parameterization, boundary layer treatment, sea surface temperature, and grid spacing. Simulations with cumulus schemes that allow more grid-scale precipitation on the 9-km grid exhibit unrealistic grid-scale overturning and slower intensification, primarily due to production of cyclonic vorticity anomalies at large radii. Use of an innermost nest with 3-km grid spacing...