Marathon Versus Sprint: Two Modes of Tropical Cyclone Rapid Intensification

Tropical cyclones undergoing abrupt intensification, commonly referred to as "rapid intensification," pose a significant forecasting challenge, fueled in part by the ongoing uncertainties in the underlying scientific understanding. To address the debates and inconsistencies prevalent in the literature, our study explores the hypothesis that distinct forms or modes of rapid intensification exist. Through a comprehensive analysis utilizing a global convection-permitting simulation and the HURDAT2 database, we present compelling evidence supporting the existence of two distinct modes of rapid intensification.

The first mode, termed the "marathon mode," is characterized by a moderately paced and prolonged intensification period. In contrast, the second mode, referred to as the "sprint mode," exhibits explosive and short-lived intensification bursts. Our findings highlight significant differences between these modes, extending beyond the duration of intensification. Variations were observed in the initial vortex structure, with the marathon mode featuring well-defined structures and the sprint mode characterized by poorly defined structures. Additionally, distinctions emerged in the nature of intensification (symmetric versus asymmetric) and prevailing environmental conditions (weak shear versus strong shear).

These disparities strongly suggest that the two modes involve distinct intensification mechanisms. Acknowledging the existence of multiple intensification modes contributes to a more nuanced understanding and improved prediction of rapid intensification. Our study not only aids in reconciling discrepancies within the literature but also emphasizes the need to recognize that rapid intensification in strongly sheared cyclones is not an exception but a typical and fundamental process. This insight holds significant implications for advancing forecasting capabilities and refining theoretical frameworks for tropical cyclone intensification.