In September 2009, Tropical Storm Ketsana (local name: TS Ondoy) hit the Manila metropolitan area (Metro Manila) and brought an anomalous volume of rain that exceeded the Philippines’ forty-year meteorological record. The storm caused exceptionally high and extensive ?ooding. Part of this study was a survey conducted along the stretch of the Marikina River, one of the major rivers that ?ooded. Postevent resident interviews were used to reconstruct the ?ooding in the absence of stream gauge data. Hydraulic and hydrologic modeling were carried out to understand the mechanism that brought the ?ood. Peak ?oods occurred at different hours along the river resulting from the transmission of water from the main watershed to the downstream areas. Modeled peak ?ood and ?ood timing coincided well with actual observations except for downstream stations where actual peak ?oods were observed to have occurred at a later time. Compounding factors such as other ?ood sources and stream back?ow could have caused this discrepancy. Nevertheless, prediction of ?ood heights and the use of the known time lag between the peak rainfall and the peak runoff could be utilized to issue timely ?ood forecasts to allow people to prepare for future ?ooding.