Variability in Coastal Flooding Predictions due to Forecast Errors during Hurricane Arthur

Storm surge prediction models rely on an accurate representation of the wind conditions. In this paper, we examine the sensitivity of surge predictions to forecast uncertainties in the track and strength of a storm (storm strength is quantified by the power dissipation of the associated wind field). This analysis is performed using Hurricane Arthur (2014), a Category 2 hurricane, which made landfall along the North Carolina (NC) coast in early July 2014. Hindcast simulations of a coupled hydrodynamic-wave model are performed on a large unstructured mesh to analyze the surge impact of Arthur along the NC coastline. The effects of Arthur are best represented by a post-storm data assimilated wind product with parametric vortex winds providing a close approximation. Surge predictions driven by forecast advisories issued by the National Hurricane Center (NHC) during Arthur are analyzed. The storm track predictions from the NHC improve over time. However, successive advisories predict an unrealistic increase in the storm’s strength. Due to these forecast errors, the global root mean square errors of the predicted wind speeds and water levels increase as the storm approaches landfall. The relative impacts of the track and strength errors on the surge predictions are assessed by replacing forecast storm parameters with the best known post-storm information about Arthur. In a “constant track” analysis, Arthur’s post storm determined track is used in place of the track predictions of the different advisories but each advisory retains its size and intensity predictions. In a “constant storm strength” analysis, forecast wind and pressure parameters are replaced by corresponding parameters extracted from the post storm analysis while each advisory retains its forecast storm track. We observe a strong correlation between the forecast errors and the wind speed predictions. However, the correlation between these errors and the forecast water levels is weak signifying a non-linear response of the shallow coastal waters to meteorological forcing.

R Cyriac, JC Dietrich, JG Fleming, BO Blanton, C Kaiser, CN Dawson, RA Luettich (2018). “Variability in Coastal Flooding Predictions due to Forecast Errors during Hurricane Arthur.Coastal Engineering, 137(1), 59-78. DOI: 10.1061/(ASCE)WW.1943-5460.0000419.

Nelson Tull wins Student Poster Award

MS student Nelson Tull won the Student Poster Award at the ASBPA National Coastal Conference 2017. This award is chosen by attendees from among all of the student posters and is reflective of both compelling research activities and excellent presentation skills.

Congratulations to Nelson!

Nelson Tull accepts the Student Poster Award during the awards luncheon at the ASBPA National Coastal Conference.

Seminar: UNC Department of Geological Sciences

News: Enhancing Storm Surge Visualization

2017/10/04 – Science Node
The aim of storm surge models: When a storm approaches, emergency managers want fast and accurate forecasts

Although our model provides water level predictions from the deep ocean all the way to the coastal floodplains, the system is limited by the model’s resolution. Topographic features at scales smaller than 500 feet, such as roadways or narrow stream channels, are often not included in the models because of the computer time needed to produce such high-resolution outputs. Because of this limitation, the extent of flooding can be underpredicted by the model.

2017/08/31 – National Consortium for Data Science
Data Fellows project aims to make storm surge predictions faster and more accurate

Continuing our North Carolina Sea Grant project and with new support from the National Consortium of Data Science, we are developing a method to improve prediction of the true flooding extent by combining the results of our model with more accurate elevation datasets.

To perform this prediction of the flooding extent, we use a Geographic Information System (GIS) called GRASS GIS that specializes in processing very large amounts of data. The project has two major objectives. The first is to process the modeled water levels and the elevation data set together, producing a map showing the extent of predicted flooding. When the modeled water levels are greater than the land elevation, flooding extends outward into neighboring, unflooded areas in the data set. By mapping the model results to the higher resolution data sets on elevation, we can create more accurate surge forecasts of overland flooding.

2017/08/08 – NC Sea Grant Coastwatch Currents
Fast, Accurate Forecasts of Coastal Flooding: Enhancing Visualization of Storm Surge Guidance to Support Emergency Managers

ncsgStorm surge models must be both fast and accurate to give coastal communities the guidance they need to prepare for and respond to a storm. Perhaps just as important is the need for these forecasts to be visualized in a way that is meaningful and useable by emergency managers.

ADCIRC forecasts are currently visualized using Kalpana, a Python script that converts the model output into formats compatible with commonly-used visualization applications such as ArcGIS and Google Earth. With support from the National Consortium of Data Science (NCDS) and in partnership with North Carolina Emergency Management (NCEM), our team has developed a new visualization method that makes use of enhanced topographic resolution along the flooding boundary. This results in modeled storm surge extending farther into estuaries and floodplains, increasing the accuracy of the forecast.