The Practical Predictability of Storm Surge Inundation from Tropical Cyclones

Predicting the hazardous conditions that people may experience due to hazardous weather often involves understanding and managing issues associated with the predictability of coupled systems. This study investigates these issues in the context of predicting storm surge inundation associated with landfalling tropical cyclones. Without timely forecasts and warnings of storm surge, it is difficult for public officials and members of the public to plan and implement evacuations and other protective actions when a hurricane approaches the coast. However, accurately predicting storm surge remains challenging, due in large part to limits in current capabilities in hurricane prediction, and the ways in which the resulting hurricane forecast errors propagate into surge predictions.

Motivated by these issues, this study aims to build understanding about the practical predictability of storm surge from landfalling tropical cyclones and the contributions of different factors to surge predictability. The research investigates the sensitivity of storm surge inundation to four storm parameters — track, intensity, size, and translation speed — and the sensitivity of storm surge forecasts to errors in forecasts of those parameters. An ensemble of storm tide (surge + tide) simulations is generated for three storms in the Gulf of Mexico, by driving a storm surge model (ADCIRC) with storms generated using best track data and systematic perturbations to each of the four storm parameters. To investigate practical predictability, the spread of perturbations was designed to represent the average error in current operational tropical cyclone forecasts.

Results show that location-specific storm surge inundation is predictable for as little as 12–24 h prior to landfall, less for small-sized storms. For the storms studied here, for which tide has a relatively small influence on surge, the practical predictability of storm surge inundation is limited foremost by errors in hurricane track forecasts, followed by intensity errors, then speed errors. Errors in forecasts of hurricane size also play an important role, especially given observational uncertainty. The results also indicate potential for increased predictability beyond 24 h for large storms by considering a storm-following, volume-integrated metric of inundation.

These practical predictability limits have important implications for storm surge prediction and risk communication, as well as for improvements in hurricane prediction aimed at improving storm surge hazard prediction. More generally, this research contributes to knowledge about predictability when coupled modeling and other tools are used to extend predictions of weather phenomena into predictions of weather-related hazards and impacts.