Why some PH storms feel more sudden

By Francis Allan L. Angelo

A 45-year analysis of tropical cyclones affecting the Philippines is sharpening scientists’ understanding of how storms evolve as they near the country’s coastlines, with University of the Philippines Diliman meteorologists warning that rapid changes in speed and intensity can compress the time communities have to prepare.

Drs. Bernard Alan Racoma and Gerry Bagtasa of the University of the Philippines Diliman College of Science’s Institute of Environmental Science and Meteorology examined 372 landfalling tropical cyclones from 1979 to 2024 and identified latitude-linked patterns that can complicate forecasting and disaster readiness.

“Storms that hit the northern part of the country tend to be stronger but slower moving. Southern storms tend to be faster and accelerate more rapidly,” Dr. Racoma explained in an interview as cited in a press release from the College of Science of UP Diliman.

“This has implications on the kinds of hazards these storms may bring,” Racoma said.

The researchers said fast-moving, rapidly accelerating storms that affect the Visayas and Mindanao can leave residents with limited lead time for evacuations, supply prepositioning and other protective actions.

They added that stronger but slower-moving cyclones that affect Luzon can prolong exposure to wind and rain, raising the risk of extended flooding and landslides when storms linger over or near mountainous terrain.

Their findings arrive as the Philippines continues to face some of the world’s highest tropical cyclone exposure, with storms regularly intersecting the country’s warning zones monitored by the Philippine Atmospheric Geophysical and Astronomical Services Administration.

Using best-track data that cover the satellite era, the study also provides a clearer sense of how long storms persist in the region’s monitoring domains compared with how briefly they directly interact with Philippine coastlines.

While tropical cyclones can remain inside the Philippine Area of Responsibility for several days, Racoma and Bagtasa found that their direct presence along Philippine coasts is brief, with a median of 21 hours before moving inland or away.

The study notes that this coastal window is the period when coastal communities can face the sharpest escalation in hazards, because storms can still be intensifying over warm water even as landfall approaches.

“In terms of geometry, medyo balingkinitan ang Pilipinas: mas pahaba ang bansa north-south, kumpara sa east-west. Since TCs usually move from east to west, they tend to cross this shorter path faster,” Dr. Racoma said in the media release, pointing out the contributing factors. “Another possible explanation is because of the loss of the fuel source—the warm ocean. TCs draw their energy from the sea, and they typically don’t like staying over land.”

The paper situates those timing constraints within a broader basin picture, reporting 1,507 tropical cyclones tracked in the western North Pacific from 1979 to 2024, with 63.77% (961) entering the Philippine Area of Responsibility and 29.00% (437) making landfall over the Philippine archipelago.

Those figures translate to an average of 9.5 landfalling tropical cyclones per year in the dataset, underscoring why forecasters and local governments are forced to manage repeated, high-frequency risks.

The study’s core contribution, the authors said, is an operationally focused look at how storms’ motion and intensity behave close to land, when warning decisions and last-mile communication become most consequential.

One of the sharpest concerns is rapid intensification, a phenomenon in which a cyclone strengthens dramatically over a short period and can outpace expectations set by earlier advisories.

“Rapid intensification occurs very fast—typically within 24 hours. We don’t yet fully understand it; even weak storms can intensify quickly. We should avoid waiting for a storm to intensify before preparing. Half of TCs that form or enter the PAR make landfall, and usually rapid intensification occurs within this region,” Dr. Racoma noted.

The paper defines rapid intensification as an increase in maximum sustained winds of at least 30 knots within 24 hours, aligning with commonly used international thresholds, and reports that many rapidly intensifying landfalling storms begin ramping up around 36 hours before landfall.

For communities, the researchers said, the implication is straightforward: preparation should begin when storms enter or form within the Philippine Area of Responsibility, rather than after the system has already intensified into a stronger category.

The accompanying landfall map and latitude histogram illustrate where first landfalls clustered from 1979 to 2024, with points tracing a broad swath along the eastern seaboard and highlighting how storm tracks repeatedly intersect coastal areas across multiple island groups.

In the paper’s latitude analysis, intensity at landfall shows a slight but statistically significant increase with latitude, while storm motion variables point in the opposite direction, with lower-latitude landfalls associated with faster movement and stronger acceleration.

Those geographic signals, the authors said, help explain why “southern storms” can feel more sudden, even when their peak winds are not necessarily higher than the strongest cyclones that strike farther north.

The work also reinforces a long-standing disaster-risk lesson in the Philippines: hazards do not end at the coastline, because slow-moving systems can sustain rainfall well after landfall, interact with topography and trigger secondary risks such as landslides.

“Characteristics and Near-Landfall Behavior of Tropical Cyclones Affecting the Philippines (1979–2024)” was published in Tropical Cyclone Research and Review, a journal focused on tropical cyclone monitoring, forecasting and research, and the study was supported by the UP Diliman Office of the Vice Chancellor for Research and Development and the Department of Science and Technology – Philippine Council for Industry, Energy, and Emerging Technology Research and Development.