The Role of Advection in Storm Surge for Hurricane Michael (2018)

Hurricane Michael (2018) made landfall near Mexico Beach, FL, as a Category 5 hurricane, with gauge-measured water levels over 4 m. Wind and pressure fields were created by blending a parametric near-field model with a gridded far-field model. Winds and modeled water levels were well validated across Michael's large impact a-ea. A detailed analysis of the coastal surge caused by Michael demonstrates that advection contributed significantly to Michael's highest water levels and the timing of the water level across a large portion of the Michael impact area. A momentum balance in a streamwise-normal coordinate system demonstrates that the advection contributions due to spatial gradients in the flow are identified with streamwise convergence/expansion of the flow field (Bernoulli acceleration) and curvature in the flow field (centrifugal acceleration). These effects are created by the regional geometry and the storm's wind field and are most likely to affect back barrier water levels and along curved coastlines. These findings provide an improved understanding of the role of advection in determining storm surge and, thus, the importance of including it in storm surge models.