AsianScientist (Oct. 24, 2025) – On May 8, 2020, hailstones larger than golf balls rained down on Cabiao in Nueva Ecija, the largest province and top rice producer of the Central Luzon region of the Philippines. Measuring over four centimeters in diameter, they were the biggest hailstones ever recorded in the country.
Thunderstorms are common across the country, driven by its tropical climate, varied terrain, and shifting wind patterns. During the Southwest Monsoon season from June to August, moist and unstable air often triggers frequent storms. Thunderstorm activity peaks in the afternoon and during the monsoon transition months – March to May and October to November. Yet despite frequent storms, hail remains a rare and little-studied phenomenon, largely due to the absence of specialized observation systems.
To fill this knowledge gap, Filipino researchers conducted the first comprehensive analysis of hail occurrences in the country, covering nearly two decades of data from 2006 to 2024.
Their findings were published in the Asia-Pacific Journal of Atmospheric Sciences.
For their research, the scientists utilized a diverse array of sources – instrument data along with local governmental records, news outlets, and geotagged social media posts. This approach was particularly beneficial due to the limited ground-based hail detection systems in the country.
The study found that hailstorms occur most often during the dry months of March, April, and May, when surface temperatures are at their peak and thunderstorms are more likely. Additionally, most events took place in the mid-to-late afternoon, the hottest part of the day.
The link between high temperatures and falling ice lies in a factor called Convective Available Potential Energy (CAPE), which measures how much energy rising air can have. When CAPE is high, warm air rises rapidly, carrying moisture into towering thunderclouds. Inside these clouds, powerful updrafts lift water droplets into colder layers of the atmosphere, where they freeze and grow into hailstones.
Dry air in the mid-atmosphere can also help hailstones reach the ground. It enhances evaporative cooling, strengthening downdrafts and speeding their descent. Because they fall faster, hailstones spend less time in warm air and are less likely to melt before landing.
While Luzon accounted for most reported hail events, larger hailstones measuring three centimeters or more were more often observed in the Visayas and Mindanao island groups.
The researchers suggest that weaker monsoon influence in these regions allows local storms to persist later into the year. The study also emphasized the importance of citizen science and public reporting in monitoring hailstorms and other severe weather threats.
As climate change increases the likelihood of extreme weather, involving the public in data collection could be crucial to enhancing early warning systems in the Philippines. The researchers also emphasized the need to strengthen the country’s weather monitoring and forecasting networks.
“Most people are surprised when hail happens because it is relatively rare in the Philippines,” said Lyndon Mark P. Olaguera, Assistant Professor, Department of Physics, Ateneo de Manila University, and senior author of the study.
“Many take photos or videos and share them online. Some are scared since it’s unusual, while others just treat it as a strange kind of rain. People usually explain it as part of strong thunderstorms, and some interpret hail as a warning or sign of climate change,” he added.
The researchers urged disaster preparedness programs to cover not just typhoons and floods, but also lesser-known threats such as tornadoes, waterspouts, and hailstorms that can take communities by surprise.
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Source: Ateneo De Manila University: Image: Eye Em/ Freepik
The study can be found at Spatiotemporal Analysis of Hail Events in the Philippines
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