A new study by Ateneo de Manila University and the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), the first of its kind in the Philippines, has found that the country’s hottest days are, in fact, more likely to produce hail.
The study, titled “Spatiotemporal Analysis of Hail Events in the Philippines,” was authored by Marco Polo Ibañez, John Manalo and Generich Capuli of DOST-PAGASA and Dr. Lyndon Mark Olaguera of the Ateneo de Manila University and the Manila Observatory.
“Most people are surprised when hail happens because it is relatively rare in the Philippines,” said Olaguera.
“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 said.
Spanning nearly two decades of data from 2006 to 2024, the Ateneo study is the first comprehensive analysis of hail occurrences in the country. Researchers found that hail events were most frequent during the dry-season months of March, April and May, precisely when surface temperatures peak and the atmosphere is primed for thunderstorms. Most hailstorms were found to have occurred during the mid- to late-afternoon, the hottest part of the day.
While Luzon recorded the most hail events overall, relatively larger hailstones were observed more in the Visayas and Mindanao. The study attributes this to the weaker influence of the Southwest Monsoon in those regions, which allows localized convective storms to persist later into the year.
For their study, Ateneo researchers relied on a wide range of sources, including instrument data, local government records, news media, and geotagged social media posts. This multi-source, crowd-informed approach proved especially valuable given the country’s sparse ground-based hail detection capabilities. This highlights the value of citizen science and public reporting in monitoring hailstorms and other severe weather hazards.
The largest hailstones ever recorded in the country fell in Cabiao, Nueva Ecija, on May 8, 2020. These ice balls reportedly reached up to 5 centimeters (2 inches) in diameter, larger than golf balls.
High surface temperatures on that day provided ideal conditions for temperature-driven air movements, or convection. Using satellite and radar data along with high-resolution weather modeling, the researchers confirmed the presence of strong updrafts and favorable conditions for hailstorms at the time.
The counterintuitive connection between heat near the ground and ice falling from the sky is partly explained by a meteorological factor known as Convective Available Potential Energy (CAPE), a measure of how much energy is available to fuel rising air.
High CAPE values indicate conditions favorable for convective activity, where hot air near the Earth’s surface rapidly rises and carries moisture into towering thunderclouds. Within these clouds, powerful updrafts can carry water droplets high enough into much colder layers of the atmosphere, where they freeze and eventually grow into hailstones.
Dry air in the mid-troposphere can increase the likelihood of hailstones surviving to reach the ground. Dry air enhances evaporative cooling, which strengthens downdrafts and accelerates the descent of hail. Because the hailstones spend less time passing through warmer air on their way down, they are less likely to melt completely before hitting the ground.
As climate change increases the likelihood of extreme weather, empowering the public to participate in data gathering may prove essential for developing early warning systems in the Philippines, the authors of the study said.
The researchers cited the need to expand the country’s weather monitoring and forecasting capabilities and recommend that local disaster preparedness focus not only on typhoons and floods but also on less familiar hazards that can catch communities off guard, such as tornadoes and waterspouts, as well as hailstorms.
