On The Formation of Hurricane Katrina (2005)

Hurricane Katrina (2005) was one of the most devastating natural disasters in the United State history. In this study, the formation of Katrina is simulated using the high-resolution COAMPS® model. The triply-nested (27 km, 9 km and 3 km resolution) model simulation, initialized on 21 August (66 h before Katrina was identified as a tropical depression), predicts successfully the location and timing of Katrina's formation in the 3-km domain. This formation, as revealed by the model simulation, is a result of the merging of an upper-level low pressure system from the northeast and an organizing vortex at low levels from the southeast. A downward propagation of the vorticity from upper levels is identified, contributing to the organization of the low-level vortex. Meanwhile, the success of the 3-km simulation stems in part from concentrated precipitations in the southeastern portion of the low-level circulation that is explicitly resolved with microphysics. The precipitation acquires banded structure at the 60 h simulation.

In the 9-km domain where the Kain-Fritsch cumulus parameterization scheme is used, there is no closed circulation relating to Katrina, due mainly to scattered and unorganized precipitation. This study shows a unique situation and delicate mechanisms for the formation of Katrina and suggests that high-resolution (~3 km) models hold the promise for understanding and predicting TC genesis.