Heavy to intense rainfall from typhoon "Ulysses" caused rivers to swell and floodwaters to rise quickly in many areas in Luzon.
Based on the 24-hour rainfall data gathered by the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) from its monitoring stations, Tanay, Rizal recorded the highest rainfall at 356 millimeters (mm), followed by Daet, Camarines Norte (271.0 mm), Infanta, Quezon (255.1 mm), and Casiguran, Aurora (238 mm).
The first 12-hour rainfall monitoring from 8 a.m. to 8 p.m. on Wednesdsay showed that the concentration of heavy rains was over the Bicol region, PAGASA weather specialist Ariel Rojas said.
Meanwhile, the second half of the 12-monitoring from 8 p.m. Wednesday to 8 a.m. Thursday showed that the concentration of heavy to intense rains moved towards the eastern portion of Luzon, and southern and central part of Luzon, he added.
He noted that the top four stations that recorded the highest amount of rainfall in the past 24 hours are in the eastern section of Luzon where the center of Ulysses made its passage.
The other stations that recorded the highest amount of rainfall were the Ambulong Station in Tanauan City, Batangas (208.4 mm), Alabat, Quezon (199.8 mm), Virac, Catanduanes (176.7 mm), Legazpi City, Albay (173.8 mm), Science Garden Station, Quezon City (153.0 mm), and NAIA Station, Pasay City (137.5 mm).
The rains brought by Ulysses was just a fraction of what tropical storm "Ondoy" dumped in September 2009 because during that time, PAGASA's Science Garden Station recorded Ondoy's 24-hour rainfall at 455 mm.
However, it is important to note that it could be possible that there were heavy rains in the Sierra Madre mountains, but PAGASA does not have a station there and that was not measured, Rojas said.
He said the closest PAGASA station is the one in Tanay, Rizal, which recorded the highest 24-hour rainfall during the typhoon's passage.
PAGASA hydrologist Richard Orendain said heavy rainfall and water from upstream have also caused the swelling of Marikina-Pasig River, San Juan River, and their tributaries.
"Sa upstream nakapagtala tayo sa Mt. Oro (Rodriguez, Rizal) ng pinakamalakas na ulan na 374 mm sa loob ng 15 hours lang, simula nung umulan hanggang matapos. Ang basin average rainfall ay 234 mm, ibig sabihin malaki ang volume ng ulan na pumatak sa basin lalo na sa upstream. (In the upstream area, we have recorded heavy rainfall of 374 mm at Mt. Oro (Roriguez, Rizal) in just 15 hours. The basin average rainfall is 234 mm, meaning a large volume of rainfall was received by the river basin especially from the upstream)," he said.
Monitoring stations in the Marikina-Pasig River showed that all seven stations recorded critical levels as easly as 9 p.m. on Wednesday at its Montalban and Burgos stations.
Three stations in the San Juan River also observed critical levels early Thursday morning.
The La Mesa Dam in Quezon City also overflowed to the nearby Tullahan River due to heavy rains from typhoon Ulysses.