Rogue Storms and Climate Chaos: How Unusual Cyclones Triggered Deadly Floods Across South and Southeast Asia

Rogue Storms, Record Rains and Widespread Devastation

In late November, climatologist Fredolin Tangang watched three tropical systems form almost simultaneously across South and Southeast Asia. The scene was striking not because each storm was exceptionally strong on its own, but because their timing, tracks and locations were highly unusual — and because they hit landscapes already saturated by earlier storms and heavy monsoon rains.

How the Disaster Unfolded

Tropical Storm Senyar developed just north of the equator in the Strait of Malacca, a rare birthplace for cyclones where the Coriolis force is normally too weak to generate rotation. Senyar then made an uncommon U-turn, moving south and east instead of the more typical westward-northward path for storms in the region. At the same time, Cyclone Ditwah struck areas of Sri Lanka rarely impacted by tropical cyclones, and Typhoon Koto moved from the Philippines toward an already waterlogged Vietnam.

These storms fell on basins already saturated by back-to-back systems earlier in November, including typhoons Fung-wong and Kalmaegi. The result was catastrophic: torrential rainfall, rapid flash floods and landslides across Indonesia, Malaysia, Thailand, Vietnam, the Philippines and Sri Lanka.

Human Toll and Record Rainfall

Disaster agency tallies compiled by news organisations put the death toll at more than 1,700 people, with hundreds still missing. Indonesia’s Sumatra was the worst hit, with at least 883 deaths reported. In central Vietnam, a meteorological station recorded 1,739 mm of rain in 24 hours — a national record and reportedly the second-highest known 24-hour total anywhere in the world.

Compound Drivers: Weather Patterns and Climate Change

Scientists say several factors combined to amplify the disaster. Two large-scale climate patterns — La Niña and a negative Indian Ocean Dipole — increased the region’s background moisture and rainfall potential. When this enhanced moisture aligned with the rare storm tracks and already vulnerable terrain and infrastructure, the result was catastrophic flooding.

Climate change is also a key amplifier. Asia is warming at nearly twice the global average, warming ocean surface temperatures provide more energy for storms, and warmer air holds more moisture, intensifying extreme rainfall events.

Local Vulnerabilities and Governance Issues

Local human factors worsened impacts: decades of deforestation and land degradation in Sumatra from illegal logging, mining and plantation expansion have made hillsides more prone to landslides. In several countries, weak infrastructure, underfunded flood defenses and concerns about corruption in flood-control projects reduced resilience and response capacity. Sri Lanka’s recent financial crisis also left limited budgetary space for preparedness and recovery.

What Experts Recommend

Experts call for two parallel responses: an urgent global phase-out of fossil fuels to limit long-term warming, and immediate, scaled-up investment in adaptation. Recommended measures include stronger early-warning systems, improved land-use planning, upgraded infrastructure, nature-based flood mitigation and sustained adaptation finance — all of which were highlighted at COP30, where leaders agreed to triple adaptation funding but fell short of a clear fossil-fuel phase-out roadmap.

Outlook

Relief and recovery are ongoing while forecasters warn of more rain for Sumatra and Sri Lanka and a fresh storm east of the Philippines. Officials and communities face the twin challenges of responding to immediate humanitarian needs and preparing for a future in which compound, record-breaking storms become more common.

“This is a human tragedy. It’s multiple conditions happening at the same time, and that makes it rather unprecedented.” — Fredolin Tangang, climatologist