To characterize the transitional region from the near-field to far-field of a river plume entering coastal waters, we conducted four surveys using an autonomous underwater vehicle (AUV) to target the outflow of the New River Inlet, North Carolina, during maximum ebb tide. The utilization of a mobile sensor to synoptically observe current velocity data in tandem with natural river plume tracers (e.g., colored dissolved organic matter, salinity) was essential in understanding the mechanisms driving the observed circulation and mixing patterns within these waters. We find that this region is regularly impacted by two primary processes: (1) the interaction of an old dredged channel plume with the main discharge and (2) the recirculation of the discharge plume by an eddy that persistently forms between the old channel and main discharge location. Wind-driven processes in the nearshore can enhance the interaction of these two plumes resulting in unstable regions where mixing of the merged plume with the receiving waters is accelerated. We also conduct comparisons between AUV velocity observations from two surveys and their corresponding velocity outputs from a parallelized quasi-3-D model. We conclude that the ability to observe the estuarine outflow transitional region at near-synoptic temporal scales and resolutions discussed in this paper is key in providing the mechanisms driving local circulation which is essential for proper parameterization of high-resolution numerical coastal models.

Tropical cyclones (TC) are some of the most intense weather systems on Earth and are responsible for generating hazardous waves on the sea surface that dominate the extreme wave climate in several regions, including the Gulf of Mexico and the U.S. East Coast. Modeling these waves is crucial for engineering applications, yet it is notoriously difficult, due to TC’s compact structure and rapid evolution in space and time relative to other weather systems. To better understand the wave structure under TCs, we use satellite altimeter data paired with TC tracks. We parse the data by TC intensity and forward translation velocity, finding evidence of extended fetch. We use the altimeter data to evaluate operational hindcasts, including the US Army Corps of Engineer’s Wave Information Study, National Oceanic and Atmospheric Administration’s National Centers for Environmental Prediction Production Hindcast, and the Institut français de recherche pour l’exploitation de la mer (Ifremer) hindcast. The Ifremer hindcast (1990–2016) is examined in detail. Near the eye in the TC-centered reference frame, we find a pattern of model underestimation in the left sector and overestimation in the right sector except near the eye where wave height remains underestimated. This pattern holds, albeit modulated, across various intensities, forward translation velocities, and radii of maximum winds; the exceptions being the fastest translating storms where the error pattern shows a trend towards overestimation in all sectors. The error patterns for intense and compact TCs exhibited more severe underestimation, which dominated the region near the TC eye.