The Unique Observations of Hurricane Michael (2018), Theory for Rapid Intensification, and Implications for Future Research

In this study, we investigate physical processes during the rapid intensification of Hurricane Michael (2018) in the Gulf of Mexico during the two days prior to landfall as a Category 5 storm. As one of the best sampled storms in history by the NOAA G-IV and WP-3D (P-3) aircraft, Michael represents the epitome of progress in obtaining observations from NOAA aircraft for current tropical cyclone research. To understand the intensity evolution, we combine the classical air-sea interaction processes within environmental shear-relative framework. Even in the presence of a 2.5 ⁰C sea surface temperature (SST) gradient in the southern Gulf of Mexico, Michael maintained a fairly symmetric precipitation and convective distribution from early in its lifecycle which helped shield the storm from dry environmental air. A favorable interaction between the SST gradient and TC is revealed, with the highest enthalpy fluxes occurring left of shear which aided the sustainment of updrafts and a recovery from low entropy (θ_e) downdraft air.

As the storm approached landfall, we relate the thermodynamic boundary layer evolution to the secondary circulation and propose how the asymmetries in the circulation insulated the boundary layer to large radii, supporting rapid energy increases and storm intensification. With the near Category 5 intensity during sampling, we link our results to previous studies that focused on these storm-scale processes at specific areas of the storm. This study underscores the importance of simultaneously measuring atmospheric and oceanographic parameters to better understand tropical cyclone structural evolution during rapid intensification and highlights some opportunities for future research using this interdisciplinary approach.