Influence of Hurricane Wind Field Variability on Real‐Time Forecast Simulations of the Coastal Environment

Abstract

Tropical cyclones are a significant and increasing natural hazard for human life and infrastructure along many coastlines throughout the world. Atlantic Ocean hurricanes deliver powerful conditions to the east and Gulf coasts of North America annually and are the most destructive natural disaster in the United States (Grinsted et al., 2019). The frequency and intensity of these storms are projected to increase with future climate warming and longer storm formation periods (Knutson et al., 2010). During these storms, large waves, high storm surge, and strong currents can combine to create a multihazard marine environment, making understanding the impacts of these events in coastal areas a vital research area (Mulligan & Hanson, 2016). Since wind forcing acts as a critical driver for coastal hydrodynamic conditions, the selection of an atmospheric forcing model represents a critical decision and several atmospheric models can be used to forecast wind conditions during a storm. Moreover, large-scale ocean models can provide predictions of surface waves, water levels, and currents. However, these forecasts lack the high resolution needed to resolve local Abstract Dynamic conditions occur in the coastal ocean during severe storms. Forecasting these conditions is challenging, and large-scale numerical models require significant computing power. In this paper, we describe a real-time modeling system (DUNEX-RT), developed in support of the During Nearshore Event experiment (DUNEX) off the coast of North Carolina, United States of America. The model is run with wave, current, and water level boundary conditions from larger-scale models, and provides 36-h forecasts of significant wave height, depth-averaged velocity, and water levels every 6-h using Delft3D-SWAN. Observations and forecasts run at different times are compared and communicated via an interactive website to verify model performance in real-time and to visualize uncertainty from changing inputs. Here, we evaluate model sensitivity to inputs from seven different atmospheric hindcasts and two atmospheric forecasts for Hurricane Dorian in September 2019. The results emphasize the importance of accurate wind forcing, with significant differences observed between the output model results for different input atmospheric forcing models and forecasts produced at different times. The best results were achieved using atmospheric forcing from the high resolution rapid refresh model, and overall, DUNEX-RT had low errors at 33 wave, water level, and current sites across the system. The model results for water levels and significant wave heights were also accurate over a longer period of 49 days. Overall, the good forecast skill achieved for the wide range of conditions over this time results suggest that this high-resolution regional approach could be applied to forecast conditions in other coastal areas. Plain Language Summary Large waves and fast flowing currents occur in the coastal ocean during severe storm events, including hurricanes. Forecasting these conditions is ...

The Effect of Regional Winds on Subtidal Along‐Inlet Currents at Oregon Inlet, NC

“…The geographic configuration surrounding Oregon Inlet, combined with prevailing winds from the southwest and northeast, maximizes fetch length over the Pamlico Sound and enhances wind induced setup/setdown (Mulligan et al, 2015;Safak et al, 2016). Previous observations and numerical simulations have shown that winds may alter water levels in the sound by more than 2 m, a magnitude that surpasses the tidal range within the sound by at least an order of magnitude (Clunies et al, 2017;Mulligan et al, 2015;Rey & Mulligan, 2021;Safak et al, 2016). Spore & Brodie, 2017;Spore et al, 2019).…”

A wave-driven surface circulation feature in Table Bay

“…It has been applied throughout the world in coastal contexts similar to this one (e.g. Mulligan et al 2008Mulligan et al , 2010Garcia et al 2015;Hasan et al 2016;Peng and Bradon 2016;de Mendoza et al 2018;Rey and Mulligan 2021). Recent coupled Delft3D FLOW/SWAN configurations have also been successfully applied to this study region by Rautenbach (2020), de Vos et al (2021) and Rautenbach et al (2020b).…”

“…These magnitudes were slightly over-predicted relative to observations but were accurate in direction and timing, and highlight the importance of wave forcing in simulating coastal currents, particularly during large wave events. Rey and Mulligan (2021) also utilised Delft3D Flow and SWAN to simulate the coastal hydrodynamics near a stretch of North Carolina shoreline during a hurricane. Although the focus of that study was on the effect of different wind forcing on the quality of the simulations, the authors also noted the importance of wave forcing on currents in certain parts of their domain, especially during large wave events.…”

Simulating the Coastal Ocean Circulation Near the Cape Peninsula Using a Coupled Numerical Model

“…This one-way nesting approach has been successfully used in other coastal areas. Most recently, a configuration of Delft3D Flow [45,46] and SWAN [47] was implemented by [48], in a similar application to this study, to assess the influence of varying wind fields on forecasts of coastal dynamics near North Carolina, USA. Boundary and atmospheric forcing from various global models were used to provide appropriately downscaled wave, current and water level estimates.…”

“…Delft3D Flow has been extensively used in ocean and coastal domains [56] and the reliability of its code variously established [57][58][59]. The model has been successfully applied in cases similar to the one in this study (e.g., [48,50,53,60,61]).…”