TYPHOON KARDING (NORU) STORM SURGE ANALYSIS USING THE COAWST MODELING SYSTEM

Abstract. The Philippines, frequently affected by typhoons, faces the hazard of storm surges. This study examined the Coupled-Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST) to simulate Typhoon Karding's September 2022 storm surge. COAWST integrates the Regional Ocean Modeling System (ROMS), Simulating WAves Nearshore (SWAN), and Weather Research and Forecasting (WRF) coupled using the Model Coupling Toolkit (MCT). Four setups were analyzed: i. ROMS only, ii. ROMS-SWAN, iii. ROMS-WRF, and iv. ROMS-SWAN-WRF, focusing on four variables: a. Surface air pressure, b. Wind speed, c. Free-surface elevation, and d. Significant wave height.

Results show that the ROMS-WRF and ROMS-SWAN-WRF setups accurately simulated Typhoon Karding's track with minimal positional error and wind speed. However, the models overestimated the typhoon's minimum air pressure with p-biases of 7.74% (i and ii), 4.1% (iii), and 3.9% (iv), and RMSE values of 68.529 hPa (i and ii), 36.744 hPa (iii), and 36.789 hPa (iv). Additionally, water levels were underestimated, with RMSE ranging from 0.31 to 0.35 meters and p-biases from −72.56% to −154.89% at Baler, Aurora validation point. At the Real, Quezon validation point, RMSE and p-bias ranged from 0.30 to 0.34 meters and −84.80% to −166.44%, respectively. Nonetheless, the models were able to simulate the storm surge and significant wave height at Baler and Real points similar to recorded data, with setup iv performing best in storm surge simulation. In summary, COAWST may be employed for typhoon simulations, with coupling being able to increase accuracy.