Instability between the Concentric Eyewalls of Hurricane Maria (2017)

The primary eyewall of Hurricane Maria (2017) exhibited an extraordinary change during an eyewall replacement cycle that caused the eyewall convection to elongate into an ellipse. As a result of this change, Maria’s intensity slightly weakened prior to landfall on Puerto Rico. Radar imagery from San Juan shows this rapid breakdown of the primary eyewall into a tangential wavenumber-two pattern. To understand the events leading to the breakdown, this work explores the unstable interaction between rings of enhanced relative vorticity in the primary and secondary eyewalls using a nondivergent barotropic model (Kossin et al., JAS, 2000). Radial gradients of vorticity in a vortex with concentric eyewalls can result in one of three types of instability: instabilities across the primary and secondary eyewalls and an instability across the echo-free moat between the concentric eyewalls. We will explore the evolution of Maria’s primary eye as it relates to all three types of barotropic instability by conducting a series of experiments in which we vary the magnitude of the relative vorticity in the rings associated with each eyewall and the radial extent of the moat.