Real-time simulated storm surge predictions during Hurricane Michael (2018)

Storm surge caused by tropical cyclones can cause overland flooding and lead to loss of life while damaging homes, businesses, and critical infrastructure. In 2018, Hurricane Michael made landfall near Mexico Beach, FL, on 10 October with peak wind speeds near 71.9 m s-1 (161 mph) and storm surge over 4.5 m NAVD88. During Hurricane Michael, water levels and waves were predicted near real-time using a deterministic, depth-averaged, high-resolution ADCIRC+SWAN model of the northern Gulf of Mexico. The model was forced with an asymmetrical parametric vortex model (GAHM) based on Michael's National Hurricane Center (NHC) forecast track and strength. The authors report errors between simulated and observed water level time-series, peak water level, and timing of peak for NHC Advisories. Forecasts of water levels were within 0.5 m of observations, and the timing of peak water levels was within 1 hr as early as 48 hr before Michael’s eventual landfall. We also examined the effect of adding far-field meteorology in our TC vortex model for use in real-time forecasts. In general, we found that including far-field meteorology by blending the TC vortex with a basin-scale NWP product improved water level forecasts. However, we note that divergence between the NHC forecast track and the forecast track of the meteorological model supplying the far-field winds represents a potential limitation to operationalizing a blended wind field surge product. The approaches and data reported herein provide a transparent assessment of water level forecasts during Hurricane Michael and highlight potential future improvements for more accurate predictions

Wind and tide effects on the Choctawhatchee Bay plume and implications for surface transport at Destin Inlet

Multiple river-dominated estuaries line the northern Gulf coast and introduce substantial density variations. Their plumes have been shown to be highly sensitive to wind and tide effects, but in studies with limited observations and idealized wind forcing. This study explores these effects with a dynamic model that can represent the full behavior from river through estuary to shelf, and for a period with extensive observations. The inner shelf adjacent to Choctawhatchee Bay, a micro tidal estuary situated along the Florida Panhandle, is subject to buoyant, brackish outflows during the ebb-phase of the tidal cycle. In December 2013, experiments were performed in this region to study mechanisms that influence near-shore surface transport. Satellite imagery showed a visible brackish surface plume at Destin during low tide. The goal of the present study is to quantify variability in the plume signature due to changes in tidal and wind forcing. Density-driven flows near Destin Inlet are modeled with the recently-enhanced, three-dimensional, baroclinic capabilities of the ADvanced CIRCulation (ADCIRC) model. Modeled tides, salinities and plume signature are validated against in-situ observations and satellite imagery. Model results reveal substantial changes in the length, width and orientation of the plume as the wind direction varied on consecutive days due to winter cold fronts. During a period of near-constant winds and variability in tidal amplitude, the model predicted a larger plume during spring tides than during neap conditions. Coriolis effects on the plume are minimized due to its small scale nature. Therefore, when the wind forcing is weak, the plume signature spreads radially from the inlet with slight preference to the down-shelf. The Choctawhatchee Bay plume is representative of other small-scale plumes formed in river-dominated and micro-tidal environments, and this work demonstrates the sensitivity of these plumes to changing environmental conditions