Despite reduction by ~ ½ in the error associated with National Hurricane Center tropical cyclone (TC) track forecasts since 1990, concurrent error associated with TC intensity forecasts has remained constant. An extreme subset of intensity change – rapid intensification (RI) – continues to surprise forecasters and thus threaten coastal communities. While operational models have become increasingly skillful at predicting synoptic steering for TCs and have thus guided the improvement of TC track forecasts, their resolutions remain too coarse to represent individual convective cores and associated microphysical processes that modulate distributions of latent heat, and thus TC intensity. Such isolated, inner-core, intense vertical velocities (i.e., convective bursts) have been detected by airborne radar and satellites and are the focus of this research, namely to investigate their distributions and associated microphysics as potential precursors to dramatic and often unexpected changes in TC intensity.
A 1-km Weather Research and Forecasting simulation, in combination with observations from the NASA Tropical Cloud Systems and Processes experiment, is used to provide statistical insight into the evolution of convective bursts and microphysical cloud properties associated with the RI of Hurricane Dennis (2005). The simulation is first evaluated against observed fields, such as reflectivity from the ER-2 Doppler radar. Contoured frequency by altitude/time diagrams are then used to characterize the vertical distributions and morphology of simulated vertical velocity, derived reflectivity, and parameterized hydrometeor mixing ratio. They show changes in the breadth of vertical velocity distributions, and thus the structure of convective bursts, that evolve prior to and during RI. The sensitivity of these findings to different, commonly-used definitions of RI is examined. It is found that the magnitude, vertical extent, duration, and inner-core proximity of convective bursts exhibit unique trends with some interpretations of RI.
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