Hurricane Maria in Puerto Rico: Structure and Intensity Evolution Prior to Landfall

Hurricane Maria made a devastating landfall on the southeast coast of Puerto Rico during the morning hours of September 20, 2017. The storm had an operational intensity estimate of 155 mph, a high-end Saffir-Simpson Category 4, and a minimum central pressure estimate of 917 mb. This makes Maria the second-strongest tropical cyclone (by wind intensity) to hit Puerto Rico since reliable records began in 1851. As a result, the storm left a trail of destruction akin to no modern-day hurricane. Given the extraordinary significance of this event for the weather community and the greater Puerto Rican society, an accurate estimate of all intensity parameters has become germane, even more than with previous weather events. Despite the loss of multiple land-based observations during the storm (e.g. official airport stations, and NEXRAD Doppler radar), a rather complete set of data from Hurricane Hunter (recon hereafter) aircraft, radar (partial record), and geostationary satellite provided vital information on the structural and intensity characteristics of Maria prior to landfall. In addition, surface pressure reports from unofficial observers in the southeast coast provided crucial information in determining an adjusted landfall pressure estimate of 924 mb proposed in this study. Such estimate was found by combining all available observational datasets. A major factor during this period was the structural reconfiguration provoked by an eyewall replacement cycle (ERC) that led to an increase in storm size and simultaneous weakening of winds from 175 mph Category 5, to upper-end Category 4 range at landfall. The ERC was well-captured by both radar and recon data, and is found to be the culprit of the widespread severe damage inflicted throughout most of Puerto Rico due to the larger radius of maximum winds. The evolution of the outer (or secondary) eyewall as it hit St. Croix, Vieques, and Puerto Rico is discussed in the context of the ERC. A second ERC is found to have occurred while Maria was moving over the northwest side of Puerto Rico, which extended the period of destructive winds in that area. Finally, the operational landfall intensity estimate is compared against available data, and the complexities of estimating damage intensity over a mountainous island like Puerto Rico are briefly explored.