A new study conducted by scientists from the Ateneo de Manila University, the Manila Observatory, state weather bureau PAGASA, and Japanese partner institutions has found that on average, tropical cyclones that stay far from the Philippines’ landmass are often more responsible for intense rainfall during the annual southwest monsoon or ‘habagat’ season, than those that directly hit the country.
The researchers analyzed 62 years of data from 1961 to 2022, focusing on rainfall patterns along the country’s western coast during the peak southwest monsoon months of July to September.
They found that on average, 33.1 percent of southwest monsoon rainfall is caused by tropical cyclones that stay offshore but enhance the habagat. These faraway cyclones pull in massive amounts of moisture from the surrounding seas, intensifying monsoon rains.
The findings counter the widely held belief that only tropical cyclones that directly hit the county pose the most serious flooding risks.
One example cited was Super Typhoon Carina (Gaemi), which stayed well away from the country in July 2024, but triggered severe monsoon rains. During the episode, Quezon City recorded nearly a month’s worth of rain in just 24 hours, leading to floods that killed 48 people and caused over P8 billion in damage, even if it never made landfall.
By separating the rainfall contributions from the monsoon itself and the direct and indirect effects of tropical cyclones, scientists hope to enhance how authorities forecast and prepare for extreme weather. The distinction is critical, especially as climate change intensifies the unpredictability of both cyclones and seasonal rainfall. The researchers stressed the need to monitor not only approaching typhoons, but also their formation and interaction with the monsoon system.
They said that better understanding of such interactions is vital for local governments and disaster response agencies, particularly in flood prone areas.
The recent floods that struck the cities of Bacolod and Talisay during the weekend are a reminder of how important that better understanding of the changing weather patterns have become. Local government units will need to work closer with the government agencies involved to come up with better warning systems because the old ways of preparing our communities only when it is in the direct path of a typhoon may no longer be enough.*
