Simulated Impacts of a Mesoscale Convective System on the Track of Typhoon Robyn

The contribution that a mesoscale convective vortex that developed within the circulation of Typhoon Robyn (1993) may have had to a significant tropical cyclone track change is simulated with a mesoscale model using initial conditions that approximate the circulations measured by aircraft during the Tropical Cyclone Motion (TCM-93) field experiment. A dry version of the PSU–NCAR Mesoscale Model is used to first investigate the dynamic aspects of the interaction. A deceleration of about 2 m s21 and then more northward movement, similar to that observed for Typhoon Robyn, could have been produced by an interaction with the mesoscale convective vortex of the type modeled in the control run. Sensitivity of the simulated track change is tested for various aspects of the mesoscale vortex and tropical cyclone. It is found that track deflections between 67 and 130 km in 18–24 h could be produced under a variety of realistic scenarios. As the mesoscale vortex is advected around the tropical cyclone by the cyclonic winds, it is also being filamented by the horizontal shear of the tropical cyclone outer winds. Whereas the rate at which the vortex is advected about the tropical cyclone is critical to the amount of curvature of the tropical cyclone track deflection, the timescale of the filamentation of the mesoscale vortex is critical to the longevity of the track deflection, and thus maintenance of the vortex is a crucial factor. For the same tropical cyclone and separation distance, th