Distant Cyclones Worsen Rain: New Findings Surprise Experts

Photo courtesy of PhilStar

In a surprising revelation, a recent study has found that tropical cyclones staying far from the Philippines' landmass significantly intensify rainfall during the southwest monsoon, known locally as the "habagat." This new understanding could reshape how experts approach cyclone and monsoon interactions.

Conducted by scientists from the Ateneo de Manila University and other institutions, the research reveals that while direct cyclone impact accounts for only 15.4% of the habagat season’s rainfall, distant cyclones contribute over twice that amount. A remarkable 33.1% of rainfall is linked to these offshore cyclones, with the southwest monsoon itself responsible for 51.5%.

Analysing data from 1961 to 2022, the study uncovers how cyclones that remain at sea still manage to draw in moisture, enhancing monsoon rains into severe downpours. This challenges the common belief that only direct hits are the main flooding threats.

A notable case is Super Typhoon Carina (Gaemi) from July 2024, which, despite not making landfall, brought massive rains to Quezon City. This caused floods that tragically killed 48 people and incurred damages exceeding 10.3 billion Thai Baht.

The study highlights how a cyclone’s "genesis point" affects its path and potential impacts. Those forming further from the Philippines often intensify the monsoon by veering northeast, while closer ones move quickly westward, having less impact.

Historically, in the wettest seasons on record like 1962, 1972, 2012, and 2018, over 2,000 millimetres of rain fell, largely due to distant cyclones. In certain cases, up to 41.5% of the rainfall was from cyclones that never touched the land but nonetheless caused significant flooding in Luzon and parts of the Visayas.

The researchers aim to enhance weather forecasting by distinguishing between rainfall from direct and indirect cyclone effects and monsoon systems. This distinction is crucial as climate change increases the unpredictability of these weather patterns.

The study notes that monitoring cyclone formation and their interplay with the monsoon is essential. This knowledge is crucial for local governments and disaster response agencies, particularly in flood-prone regions like Metro Manila, Zambales, Ilocos, and Palawan.

By refining these forecasting techniques, scientists hope to improve preparedness strategies, ultimately reducing the risk and impact of future flooding events.

  Adapted by ASEAN Now from PhilStar 2025-07-15