Investigating Potential Scenarios from Probabilistic Storm Surge Guidance

The Storm Surge Unit (SSU) at NOAA’s National Hurricane Center (NHC) is responsible for issuing storm surge watches and warnings when tropical cyclones threaten the U.S. Gulf and East Coasts, as well as Puerto Rico and the U.S. Virgin Islands. The probabilistic storm surge model (P-Surge) is the main source of guidance for issuing these warnings. The P-Surge ensemble is centered on the current NHC Official forecast and is perturbed (e.g., along- and cross-track spread) using the 5-year average of NHC Official forecast errors. The P-Surge 10% exceedance threshold is used to guide the extent and timing of the storm surge watch/warning and is the underlying data of the NHC’s Potential Storm Surge Flooding Map.

While the exceedance probabilities are extremely important for evaluating the overall risk, SSU forecasters must subjectively estimate which types of storms cause an extreme surge at a particular location. The P-Surge ensemble can have up to 1200 storm scenarios and it may be valuable to objectively investigate the ensemble realizations that primarily contribute to 10% exceedance levels at locations of interest. The goal is to quickly identify location-specific track, intensity, and storm structure vulnerabilities and facilitate decision-making during fast-paced storm surge operations. A barrier to this work is that the large number of ensemble realizations presents a data storage challenge, and outputs must be streamlined for effective use by forecasters. This study explores how additional guidance could be efficiently derived from the P-Surge ensemble to help localize storm surge risk.