Simulating the formation of Hurricane Katrina (2005)

The formation of Hurricane Katrina (2005) is simulated using COAMPS1 with high resolution (27 km, 9 km and 3 km grid spacing). Whereas most Atlantic hurricanes form in conjunction with easterly waves, no clear synoptic-scale tropical disturbance was evident as a precursor for Katrina. The triply-nested simulation, initialized 66 h before Katrina was identified as a tropical depression, successfully predicts the location and timing of Katrina's formation in the 3 km domain. The organization of the cyclone is associated with concentrated precipitation resolved with microphysics in the southeast part of the circulation. The storm does not form in the 9 km domain when the Kain-Fritsch cumulus scheme and the microphysics are used. However, a separate simulation using microphysics alone in the 9 km domain captures Katrina's formation, though with less organized structure. This study suggests that explicitly resolving clouds in high-resolution models holds promise for predicting tropical cyclone (TC) formation.