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Abstract
The Philippines has an average of twenty tropical cyclones entering the Philippine Area of Responsibility every year, with about six to nine making landfall. In September 2011, Typhoon Nesat (Pedring) passed about 200 km north of Manila Bay with maximum sustained wind speeds of 46.3 m/s (CAT 2), yet it was one of the most destructive storms to affect the coastal areas of Metro Manila. In order to further understand the storm surge hazard for Metro Manila, and why Typhoon Nesat was so destructive, both an analysis of historical records and numerical modeling were undertaken. The historical analysis revealed that neither the most intense (with intensity defined as the maximum sustained wind speed of the cyclone) nor the storms that passed closest to the site generated the largest values of surge. Numerical simulations of the storm surge were completed using wind and pressure input data from the Holland vortex model, the Rankine vortex model and reforecast data from the National Center for Environmental Prediction (NCEP) model. NCEP data were found to better represent the wind field in the vicinity of Manila Bay, as it accounted for interaction between Typhoon Nesat and the SW monsoon winds. Neglecting these interactions, the storm surge simulations with analytical vortex models underestimated predicted surge values by more than five times, while the simulations with NCEP data accurately modeled the surge. The study highlights the need for improved storm surge warning systems that account for factors other than the cyclone's maximum sustained wind speeds, which can affect the severity and duration of surge events.