Hurricane Maria Rainband Evolution and Their Potential Linkage to a Second Eyewall Replacement Cycle Over Puerto Rico

Hurricane Maria (2017) brought unprecedented modern-era devastation to Puerto Rico (PR), and it is the second-strongest tropical cyclone (TC) by wind intensity on record there. The Saffir-Simpson Category 4 (155 mph; 69 m/s) crossed the main island from southeast to northwest, bringing the core of extreme winds through the island’s densely populated areas, exacerbating the magnitude of the damage. In the hours prior to landfall, an eyewall replacement cycle (ERC) ensued as the TC was nearing the coast. This process led to a weakening from Category 5 (175 mph; 78 m/s) to Category 4 (155 mph; 69 m/s) by landfall. In addition, the ERC was responsible for a larger area of extreme winds affecting more PR residents and for a longer time exposure to such weather conditions. Available aircraft reconnaissance (recon), radar, and satellite data made for a good documentation of the pre-landfall ERC. However, little is known about the storm’s inner-core as it crossed PR. In an attempt to shed some light on this issue, we discuss the occurrence of a second ERC as Maria was moving through and away from PR. Recon and radar data reveal strong rainbands wrapping around the outer eyewall while nearing landfall. Surface observations in nearby Culebrita Island confirm recon measurements of surface Category 3 intensity winds occurring outside of the outer eyewall, in the area of the innermost rainband. Such an expansion in the tangential wind field where induced mainly by the first ERC. However, the observation of an additional ERC as Maria was departing the northwest coast of PR lead to a focus on these bands as potential precursors to the second ERC as early as before landfall. The consolidation of a new eyewall as Maria was moving away from PR prolonged the period of destructive winds, mainly in the western half of the island. Several social media accounts from this area mentioned the pass of this feature as it brought a notable increase in destructive winds and heavy rain several hours after the original eyewall had moved away from those locations. After radar loss just before landfall, satellite data and surface observations, and recon (overwater) became germane to the understanding of Maria’s structure. The occurrence of an ERC as a TC is moving over land makes this an interesting case for review, especially in light of recent advances in our understanding of TC inner-core dynamics.