THE FORMATION OF HURRICANE-FREDERIC OF 1979

A high-resolution global model forecast of the formation of Hurricane Frederic of 1979 is analyzed by means of several diagnostic computatio ns on the model's output history. The formation is addressed from an a nalysis of limited-area energetics where the growth of eddy kinetic en ergy is examined. The question on internal versus external forcing dur ing the formative stage of the hurricane is explored by means of the K uo-Eliassen framework for the radial-vertical circulation of the hurri cane. The intensity of the predicted hurricane is diagnosed from a det ailed angular momentum budget following the three-dimensional motion o f parcels arriving at the maximum wind belt. Overall, the successful s imulation of the hurricane has enabled us to make such a detailed diag nosis of the predicted hurricane at a high resolution. The principal f indings of this study are that a north-south-oriented heating function maintained a zonal easterly flow that supplied energy barotropically during the growth of an African wave. The growth of eddy kinetic energ y is somewhat monotonic and slow throughout the history of the computa tions. The initial development of the easterly wave appears to be rela ted to the widespread weak convective heating that contributes to a co variance of heating and temperature and of temperature and vertical ve locity. The hurricane development period is seen as one where both the barotropic and convective processes contribute to the growth of eddy kinetic energy. During this developing stage, the growth of radial-ver tical circulation is largely attributed to convective, radiative, and frictional forcings. The role of eddy convergence of momentum flux app ears to be insignificant. The intensity issue of the storm (maximum wi nd of the order of 37 m s-1) was addressed by means of a detailed angu lar momentum budget following parcel motion. The pressure torque in th e model simulation had a primary role in explaining the intensity of t he predicted storm. It is only in the storm's inner rain area where th e frictional stress becomes quite large. But at these small radii the frictional torque is still smaller compared to the contribution from t he (small but significant) azimuthal asymmetries of the pressure field and the resulting pressure torques.