TWO KEY alerts from the state weather agency have served as the public’s main sources of information about weather conditions, with prolonged southwest monsoon rains or habagat causing heavy flooding and cancellation of classes and government office operations this week.
Why this story matters: As of Thursday morning, July 24, “Emong” has strengthened from a severe tropical storm into a typhoon. “Dante,” a tropical storm, continues to intensify the habagat rains. A low-pressure area just outside the Philippine Area of Responsibility has developed into a tropical depression.
Expert takes: The Varsitarian interviewed two Pagasa weather specialists, Veronica Torres and Ana-Clauren Jorda, and senior weather forecaster for the National Capital Region Julie Nimes, to understand how these alerts work and how the public can properly interpret them.
Pagasa’s alerts: The Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) Weather and Flood Forecasting Center, through its Weather Division and Regional Services Divisions, typically issues two rainfall-related alerts: weather advisory and heavy rainfall warning.
A weather advisory is a forecast issued every six hours. It estimates rainfall in the next 24 hours, often across large areas such as provinces or regions.
This advisory uses a color-coded system based on the total amount of expected rainfall:
- Yellow: 50–100 millimeters (mm)
- Orange: 100–200 mm
- Red: More than 200 mm
A heavy rainfall warning is based on real-time conditions. Julie Nimes, Pagasa senior weather forecaster for Metro Manila, said this warning is issued every three hours. It reflects rainfall already happening or about to occur and is more localized, often down to the municipality level.
The warning also uses a three-color system, but based on observed rainfall per hour:
- Yellow (Be Alert): 7.5–15 mm
- Orange (Be Prepared): 15–30 mm
- Red (Take Action): More than 30 mm
A yellow warning means those in low-lying areas should be alert for possible flooding, while orange indicates that communities should be ready to respond. A red warning indicates a threat, meaning communities should already be taking action.
The logic: The weather advisory aims to give local governments enough time to prepare. Heavy rainfall warnings, however, are meant to alert communities to respond to urgent and evolving situations.
- “Naka-base po ito sa real-time monitoring,” Nimes said. “Kung makikita na namin na malalakas ang papasok na ulan, tina-taas na agad ang warning para maka-respond ang mga komunidad.”
Forecasts made visual: To make rainfall alerts easier to understand, Pagasa has shifted from text-only bulletins to color-coded maps.
- “Actually, po, ‘yong weather advisory natin dati ay naka-text lang. Pero ngayon, minamapa na po natin ito,” Torres said.
- “Ngayon, nilalagay na natin sa mapa ng Pilipinas at kinukulayan na para mas madaling makita kung aling areas ang naka-50 to 100, 100 to 200, at more than 200 mm,” she added.
Shades of blue: Maps now use sky blue for areas expecting rainfall and dark blue for areas already affected.
- “Expecting” indicates projected rainfall in the next few hours.
- “Affecting” means rainfall is already occurring in that area.
Damage: The National Disaster Risk Reduction and Management Council reported over 2.7 million people, or 765,869 families, affected in 65 provinces as of July 23. At least 147,521 individuals are staying in 1,117 evacuation centers, while nearly 98,000 others have sought shelter elsewhere.
What’s next: On July 22, Manila Mayor Isko Moreno placed the City of Manila under a state of calamity, joining 40 other cities and municipalities. This allows the release of calamity funds. Pagasa will continue to issue forecasts through platforms like radio, Facebook, and YouTube. Marielle F. Pesa and Justin Jacob S. Urag
