Code 613.1 Branch Seminar: Weixing Shen

University of Maryland, ESSIC
Due to the constant improvement in observational and dynamic systems, hurricane track prediction has been significantly improved for the recent decades. But this is not the story for hurricane intensity prediction which is now one of the most imperative challenges in hurricane prediction. As a matter of fact, current operational prediction of hurricane intensity still relies heavily on empirical and statistical models. A simple physical model for hurricane intensity in terms of energetics has been developed in hope that such a simple model can help to better understand the roles of some processes/factors in determining hurricane intensity and hopefully provide useful guidance on how to analyze hurricane observational data and numerical weather prediction (NWP) model products towards NWP model improvement for intensity prediction. The model considers storm-scale kinetic energy balance, borrowing the concept that the total kinetic energy converted from sea surface entropy fluxes and internal potential energy or CAPE should be perfectly balanced by the total surface dissipation for a steady and barotropic hurricane or when a potential intensity is achieved. With this model, the roles of environmental SST, CAPE and some hurricane structural features in determining hurricane potential intensity were investigated. The results indicate that a larger-size hurricane tends to have a higher potential intensity and that a moderate CAPE may lead to the steady state (or potential intensity) appreciably different from the otherwise surface entropy flux conversion and surface dissipation balanced state. The results also show that hurricane potential intensity seems less dependent on the underlying SST than was indicated by other potential intensity models. A simple model for hurricane intensity prediction was also developed based on the energetics model. It is hypothesized that hurricane intensity change is solely determined by the initial hurricane state and its future large-scale environmental conditions, implying that the sub-grid scale processes, if important, are strongly conditioned by these large-scale conditions. Like in other simple intensity models, it is assumed that storm track and large-scale environmental conditions can be well predicted by the NWP models since the track and its environment prediction serve as the base for intensity prediction in both the NWP models and the empirical intensity models. The model was tested for hurricanes Humberto and Felix (September, 2001). A series of runs starting from different times were performed with observed initial storm conditions and NWP model-predicted future environmental conditions as the model inputs. The results by this model are fairly consistent with observations.