A closer look at why the rainfall warning came late, and why classes couldn’t have been suspended sooner
There were no rainfall warnings hanging over Metro Manila in the early hours of Wednesday, September 9, even as clouds gathered thick and low across the region overnight.
Then, without a single alert to prepare for it, heavy rain suddenly poured down across the metro, catching commuters mid-commute and students already boarding jeepneys, tricycles, and school service vans.
Only at 6:30 AM did PAGASA finally issue a yellow rainfall warning, by which point classrooms across several cities were already filling with students who had left home hours earlier.
By 7:30 AM, local government units watching the rain intensify on the ground began suspending classes, some acting on their own well before PAGASA’s next warning came through.
At 8:00 AM, PAGASA escalated to an orange rainfall warning over Metro Manila, and a wave of additional local governments moved quickly to suspend classes at every level right after.
Some students who had already reached school that morning were sent back home mid-morning, the warning only catching up to them once the whole capital region was already under heavy rainfall.
PAGASA-NCR Regional Services chief Engr. Lorenzo Moron said the agency’s rainfall warning system does not activate on forecasted risk alone, but only once actual rainfall crosses specific measured thresholds.
“Kailangan maintindihan din ng publiko na ang binibigay ng Regional Services Division ng PAGASA sa amin sa region ay yung rainfall warning na 3-hour duration,” Moron said, explaining the system’s mechanics.
Yellow covers 7.5 to 15 millimeters of rain in an hour, Orange covers 15 to 30 millimeters, and Red is reserved for anything beyond 30 millimeters in an hour. This threshold-based design explains why the system stayed completely silent through 3:00 AM, 4:00 AM, 5:00 AM, and 6:00 AM, even as Wednesday’s rain conditions were quietly building overnight.
A separate tool, PAGASA-NCR’s daily impact-based forecast issued at 3:00 AM, had already rated Metro Manila’s 5:00 AM to 11:00 AM window as facing significant impact at medium to high likelihood, according to the agency’s own risk assessment released that morning.
Under PAGASA’s own national impact table, a “significant” rating means disruption to the majority of daily routines, moderate to extensive damage to buildings, and serious injuries becoming a real possibility for the areas affected, and it existed nearly three and a half hours before the first color-coded rainfall warning appeared on anyone’s radar.
Moron, however, cautioned against treating that early guidance as anything close to a guarantee, drawing a firm line between what PAGASA can forecast in advance and what it can actually confirm as it happens.
“Hindi talaga siya yung tipong ito na mangyayari. More on indicative,” Moron said, describing how PAGASA frames its earliest morning guidance for local officials and the riding, working public alike.
PAGASA’s Weather Advisory No. 69, issued the night before at 11:00 PM, had also not listed Metro Manila among the areas expected to see heavy rainfall the following day.
Moron said the rainfall warning updates every three hours and applies city by city, allowing PAGASA to sharpen its guidance as conditions shift through the course of a single day.
Even with that tighter update cycle, he said, a single localized thunderstorm can flood one Metro Manila city completely while a neighboring one stays bone dry within a matter of minutes.
“Nagda-drive tayo from San Jose del Monte to Cubao. Paglabas natin ng San Jose del Monte ang ganda ng panahon, pagbaba natin ng Fairview biglang kumulog, kumidlat,” Moron said, describing that pattern.
Metro Manila’s vulnerability to flooding runs deeper than any single morning’s timeline, said Mines and Geosciences Bureau (MGB) senior geologist Engr. Mitch Mendoza, tracing the problem back to the region’s underlying geology and terrain.
“The National Capital Region is fundamentally an isthmus zone that is formed through deltaic, fluvial, and lacustrine processes,” Mendoza said, describing Metro Manila as a narrow strip of land under constant pressure.
She said the region sits wedged tightly between Manila Bay and Laguna de Bay, its western coastal cities built on loose, unconsolidated sediment that lets rainwater rush in and out fast, while further east, the Marikina Valley occupies a block of earth that dropped between two active fault systems, forming a natural basin that funnels water down from the Sierra Madre.
Parts of the region have also physically sunk over the decades, Mendoza said, a slow slide caused by natural sediment compaction layered on top of decades of groundwater extraction and heavy construction.
Beyond the ground itself, Mendoza said local governments remain too tethered to national guidance instead of trusting their own read of ground conditions when the moment comes to act.
“Hindi pa natin sila hinahayaan to decide on the suspension and cancellation of government work based of course on the actual ground situation,” Mendoza said, describing that persistent institutional hesitation.
That hesitation showed clearly on Wednesday, when suspensions rolled out unevenly across the metro, arriving city by city only after each local government watched the rain fall for itself.
Moron said PAGASA is now working through the Metro Manila Disaster Risk Reduction and Management Council to link individual local government sensor networks directly into the agency’s own forecasting models.
“Pero sa ngayon kasi dahil hindi siya integrated, so we work in silos in terms of monitoring,” Moron said, describing the current disconnect between national forecasters and city-level disaster offices.
Forest Management Bureau (FMB) assistant director Atty. Ray Thomas Cabigting said Metro Manila’s terrain functions as a natural drainage system, one designed by nature to move water downhill toward its rivers and basins, never to eliminate flood risk outright.
He said the region’s forests along the surrounding mountains play a direct role in that system, slowing the force of rainwater as it falls and directing its flow before it can strike populated ground below with full impact.
That natural design, Cabigting said, makes some degree of flooding unavoidable no matter how well the terrain or forest cover is managed, since the risk can be reduced but never brought down entirely to zero.
What compounds the problem, he said, is the lack of coordination between neighboring local governments once a suspension decision is made in one city but not immediately relayed to the next.
“Dapat po lahat po tayo ay nag-uusap-usap at nagtutulungan para po hindi na nagco-commute mula Bulacan hanggang Visayas Avenue just to find out na sa pagdating po niya ng Quezon City Circle ay suspended na po pala ang trabaho,” Cabigting said.
