An Analysis of the Unexpected Weakening of Hurricane Delta (2020) Using Coamps-TC and Aircraft Observations

Hurricane Delta (2020) was a category 4 major hurricane that rapidly intensified in the Caribbean Sea after genesis, but then weakened unexpectedly to category 1 intensity before making landfall on the Yucatán Peninsula. This study uses a COAMPS-TC model simulation of Delta along with NOAA aircraft observations of the storm to examine the factors that led to its weakening, specifically focusing on the transport of dry environmental air into the storm’s inner core (i.e., ventilation). The results show that during its weakening phase the hurricane vortex had a large tilt that exposed the inner core to the surrounding environment, providing a pathway for ventilation. A comparison of ventilation between the weakening period and a later intensification period showed larger values of ventilation near the inner core when the storm was weakening. Additionally, strong horizontal gradients in upward and downward motion within the eyewall likely contributed to weakening by mixing the dry air transported into the storm by ventilation throughout the center. The results from the simulation are compared with observations from the NOAA WP-3D tail Doppler radar to show that the model provides an accurate simulation of Delta.