Idealized modeling of hurricane-trough interaction: analyses of storm structure and intensification

Using a non-hydrostatic, three dimensional model (MM5) on fine horizontal resolution (5 km) and explicitly resolved convection, we investigate the challenging problem of hurricane-trough interaction. Three different idealized upper levels lows will be allowed to interact with an idealized tropical cyclone. The upper lows vary in intensity measured in terms of PV. In each case the initial tropical cyclone is the same. The low is initially positioned 800 km west of the storm. A weakly sheared environment allows the systems to approach one another. After approximately 48 h signs (eddy angular momentum fluxes and vertical shear increase) that the two systems are interacting become evident. As the systems interact, the storms temporarily cease intensification. After this period the storms interacting with the 2 weakest upper lows resume to intensify slowly. The strongest upper low, on the other hand, somehow causes the hurricane to intensify more rapidly. At the end of the simulation period there is an entire Saffir-Simpson category of difference between the intensities of the two weak low cases and the strong low case. Therefore, if landfall were to occur at this point, the consequences would vary substantially. This work takes a first step towards providing forecasters with information on how to distinguish between 'good' and 'bad' troughs. The 'good' trough in this case (i.e. good for intensification) is a strong system with deep vertical penetration and a horizontal scale almost twice that of the hurricane. Merger of the two systems not only reduces vertical shearing effects, but possibly triggers secondary eyewall cycles in the hurricane which are observed after the merger takes place. The structures of the hurricanes in each of the three cases will be presented and compared to the structure and evolution of hurricanes in vertically sheared flow.