NUMERICAL PREDICTION OF HURRICANE-OPAL

The main theme of this paper is on the intensity forecast of a hurrica ne (Opal) and interpretation of factors contributing toward it. The pa per illustrates the results oi assimilation and prediction for Hurrica ne Opal of 1995 from a very high-resolution global model. The assimila tion makes use of a detailed physical initialization that vastly impro ves the nowcasting skill of rainfall and the model-based outgoing long wave radiation. Some of the interesting aspects of Hurricane Opal's hi story occurred between 1200 UTC 1 October 1995 and 1200 UTC 5 October 1995. During this period the storm made landfall over the Florida panh andle. The storm reached maximum wind speed of over 130 kt on 4 Octobe r 1995. The intensity issue of Opal has drawn much attention. Issues s uch as the potential vorticity impact from a middle-latitude trough, t he angular momentum of the lower-tropospheric inflow layer, the warm o cean temperature anomalies of the northern Gulf of Mexico, and the pos sible role of mesoconvective concentric eyewall are discussed in this paper. The main finding of this study is that a reduction of the gradi ent of angular momentum occurs above the regions of maximum convective heating. This contributes toward stronger cyclonic spinup of parcels that enter the storm environment from the middle latitudes. Another ma jor contributor is the import of angular momentum along the lower-trop ospheric inflow channels of the storm. These channels were found to be open, that is, uncontaminated with a plethora of deep convection and heavy rain. This permitted the high angular momentum to advance toward the storm's interior thus contributing to its intensification.