Identifying the Earliest Signs of Storm Impacts to Improve Hurricane Flooding Forecasts

One of the most unpredictable and deadly parts of a coastal storm is the storm surge, which can cause devastating flooding of coastal regions, and can result in loss of property and life. Storm surge is a result of winds pushing water from the nearshore ocean to rise above regular tide levels. Storm surge can have a short duration; elevated water levels are limited to when the storm winds are strongest at the coast, typically for a few hours as the storm makes landfall. This short duration is a challenge for predictions of when storm surge will start, how long it will persist, and which regions will be flooded.

To predict storm surge and its associated flooding in coastal areas, numerical models must have a detailed representation of the impacted region, and thus be accurate, without having too much detail, which can limit efficiency. This research examines the use of a multi-resolution approach to improve both efficiency and accuracy. The key idea is that, as a storm travels across the ocean, it will affect different regions at different times. Early on, as the storm moves in open water and far from people, efficiency is more important in the model predictions. But as the storm moves toward the coast, it becomes necessary to have a higher accuracy near coastal communities and infrastructure. This research examines the use of multi-resolution simulations in which, as a storm travels along its track, the model ‘switches’ from lower resolution in open water to higher resolution as the storm moves closer to land. The main research question is to determine when is it most beneficial to switch resolutions by determining when storm effects are first seen at the coast.

This research will explore the arrival of storm effects for Florence, which made landfall along the North Carolina coast during September 2018. It is an ideal storm for this research as its track was shore-normal, and thus its coastal effects increased as it approached landfall. This will allow for investigating the most optimal switch by focusing on a single switch between a lower-resolution mesh to a higher-resolution mesh. The switches will be initiated by several triggers, including wind speeds and water levels at the coast and inland locations, and with several lead times, including near and several days before landfall. Model performance will be quantified via comparisons to observations of storm effects in the region, as well as to a single, high-resolution simulation for the full storm. It will be shown that switching from a coarse resolution mesh to a fine resolution mesh will lead to an increase in efficiency gains across all switching simulations with the most optimal switch time resulting in the most accurate predictions of water levels as compared to our full high-resolution simulation.

The results of this research will provide valuable contributions to forecasters working tirelessly during hurricane season to produce accurate and efficient predictions of coastal flooding impacts. With this information, real-time forecasts can be delivered sooner to emergency managers for informing evacuation zones, thus saving lives.

AC Poisson (2021). “Identifying the Earliest Signs of Storm Impacts to Improve Hurricane Flooding Forecasts,” North Carolina State University.

Posters: EWC Symposium 2020

A Poisson, JC Dietrich “Improving ‘sub-grid’ representation in the SLOSH model. Environmental, Water Resources, and Coastal Engineering Research Symposium , North Carolina State University, 6 March 2020.

Improving ‘sub-grid’ representation in the SLOSH model.

CA Rucker, N Tull, JC Dietrich, R Luettich, R Cyriac. “Improving the accuracy of a real-time ADCIRC storm surge downscaling model. Environmental, Water Resources, and Coastal Engineering Research Symposium , North Carolina State University, 6 March 2020.

Improving the accuracy of a real-time ADCIRC storm surge downscaling model.

JL Woodruff, JC Dietrich, AB Kennedy, D Wirasaet, D Bolster, Z Silver, RL Kolar. “Improving predictions of coastal flooding via sub-mesh corrections.Environmental, Water Resources, and Coastal Engineering Research Symposium, North Carolina State University, 6 March 2020.

Improving predictions of coastal flooding via sub-mesh corrections.

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PREEVENTS Project Meeting in Chicago

Several CCHT members visited Chicago to meet with collaborators from Notre Dame on our NSF PREEVENTS project. The meeting was held in the Chicago campus of the Notre Dame College of Business, located on Michigan Avenue in downtown. Despite the great views from the venue, we had a productive meeting!

Johnathan Woodruff, Zachariah Silver, Casey Dietrich, Autumn Poisson, Andrew Kennedy, Amirhosein Begmohammadi, Thomas Sherman, and Dam Wirasaet.

Analytic Solution for Wind-Driven Setup

In their manuscript “Analytic Solutions for Computer Flow Model Testing,” Lynch and Gray present solutions for water levels and depth-averaged velocities, for tidal and/or wind forcing, and for Cartesian and polar domains. These solutions have been useful for model validation, especially for tides, and especially within the ADCIRC community — the first example problem in the ADCIRC documentation is based on one of their solutions. That problem, for tidal flows in a polar domain, has been used to validate several model advancements over the years.

However, we found an error in their solution for wind-driven setup on a polar domain. It appears to be a typographical error — the variables are not updated correctly at the last step, when the solution is generalized for a wind with arbitrary direction. This solution is not used frequently, and we did not find a correction to this error in the literature (although we were unable to access every subsequent manuscript that cited the Lynch and Gray solution). So we are documenting it here.

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Presentation: HPC User Research Symposium