Fast Storm Surge Ensemble Prediction Using Searching Optimization of a Numerical Scenario Database

Accurate storm surge forecasts provided rapidly could support timely decision-making with consideration of tropical cyclone (TC) forecasting error. This study developed a fast storm surge ensemble prediction method based on TC track probability forecasting and searching optimization of a numerical scenario database (SONSD). In a case study of the Fujian Province coast (China), a storm surge scenario database was established using numerical simulations generated by 93 150 hypothetical TCs. In a GIS-based visualization system, a single surge forecast representing 2562 distinct typhoon tracks and the occurrence probability of overflow of seawalls along the coast could be achieved in 1-2 min. Application to the cases of Typhoon Soudelor (2015) and Typhoon Maria (2018) demonstrated that the proposed method is feasible and effective. Storm surge calculated by SONSD had excellent agreement with numerical model results (i.e., mean MAE and RMSE: 7.1 and 10.7 cm, respectively, correlation coefficient: >0.9). Tide prediction also performed well with MAE/RMSE of 9.7/11.6 cm versus the harmonic tide, and MAE/RMSE of phase prediction for all high waters of 0.25/0.31 h versus observations. The predicted high-water level was satisfactory (MAE of 10.8 cm versus observations) when the forecasted and actual positions of the typhoon were close. When the forecasted typhoon position error was large, the ensemble surge prediction effectively reduced prediction error (i.e., the negative bias of -58.5 cm reduced to -5.2 cm versus observations), which helped avoid missed alert warnings. The proposed method could be applied in other regions to provide rapid and accurate decision-making support for government departments. SIGNIFICANCE STATEMENT Typhoon storm surge can be a serious hazard to life and infrastructure in coastal areas. However, accurate storm surge prediction is difficult owing to the uncertainty associated with typhoon landfall forecasting. We proposed a multitrack prediction scheme based on a typhoon prediction probability circle. For effective and accurate operational application, we proposed a query optimization method based on a precalculated numerical scenario storm surge database. This method can generate a set of storm surge predictions using 2562 possible typhoon tracks within 2 min. This simple and efficient method could provide accurate and timely results to support decision-making in an operational application.