The evolution of hurricane-like vortices in three-dimensional flow

Warm ocean temperature and low vertical windshear are favorable conditions for hurricane intensification. Interaction of hurricanes with upper-level low pressure systems is also believed to affect hurricane intensification. Hurricane-low interaction dynamics are complex and poorly understood, thus affecting hurricane forecasting and emergency management.; This idealized, numerical modeling study investigates hurricane-low interaction. First, the effects from the vertical windshear associated with the lows are assessed. A hurricane in low vertical wind shear becomes less intense than an identical hurricane in quiescent flow. Higher values of vertical wind shear further lowers hurricane intensity and forces strong asymmetries in the storm. This asymmetric structure prevents the hurricane from intensifying via efficient symmetric vortex dynamics. Instead, asymmetric intensification processes take over.; In part II of this work the same hurricane interacts with three different upper level low pressure systems. The lows differ in intensity and size. Initially, large shear causes hurricane intensification rates to decrease. The weaker two lows are stretched in a horizontal direction by the hurricane flow, but remain present in a deformed state during most of the simulation, forcing asymmetric hurricane intensification dynamics. The hurricane intensifies slowly. The strongest of the three lows is less affected by the circulation of the hurricane and instead merges with the hurricane at mid-levels. The upper level remnants of the low are advected away. Symmetric intensification dynamics then take over, and larger intensification rates occur earlier in the simulation. Hence, this storm becomes more intense at the end of the simulation than the other two cases.; The dynamics of the surrounding atmosphere are concluded to have a strong impact on hurricane intensity. Even low shear prevents the hurricane from making full use of its available thermodynamic energy. Large shear and interaction with upper lows force less efficient, asymmetric hurricane intensification dynamics. Hence interaction with lows changes the path to, but not the value of the ultimate hurricane intensity. Therefore, when forecasting hurricane intensity at landfall, the timing of landfall relative to interaction with the low is crucial. Furthermore, the relative intensity of the low compared to the hurricane determines the length of the interaction.