Diagnosing development. II - A study of rapid cyclone development using analyzed data fields

A diagnosis is presented of the explosive development phase of a cyclone that occurred over the southeastern U.S. during the 24 hour period 1200 GMT January 20 to 1200 GMT January 21, 1979. The Zwack-Osossi development equation is extended to incorporate geostrophic and ageostrophic forcing of the basic development parameter, geostrophic vorticity tendency. This equation yields reasonable comparability with observed geostrophic vorticity changes and shows positive vorticity advection, latent heat release and thermal advection to be the primary development mechanisms.