Why the East Sea is seeing its busiest storm season in 30 years

Since January, the basin has spawned 15 storms and five tropical depressions, a level seen only once in the past three decades, back in 2017. The impacts across Vietnam have been devastating: 409 people dead, 727 injured, and economic losses exceeding VND85 trillion (US$3.2 billion). And the season still is not over. Meteorologists warn that another storm or tropical depression could form before year's end.

So why is 2025 so extreme?

According to Truong Ba Kien, deputy director of the Center for Meteorological–Climate Research under the Vietnam Institute of Meteorology, Hydrology and Climate Change, the answer lies in the West Pacific, the planet’s most prolific typhoon factory, and in a series of overlapping climate drivers that all tipped the scales toward more storms, not fewer.

The central Pacific has remained cooler than normal for months, sitting in a "cold-leaning neutral" state. It is not a full La Niña, but it behaves like a weaker version of one. When these waters cool, storm systems tend to form farther west and drift toward Southeast Asia. That raises the odds of cyclones entering the South China Sea, or forming directly over it.

Meanwhile, the Indian Ocean Dipole has swung into a strongly negative phase, warming waters around Indonesia. That warmth fuels deep convection and thick clouds, sending moisture surging toward Southeast Asia and creating a fertile zone where atmospheric disturbances can grow into tropical cyclones.

Another major player this year: the Madden–Julian Oscillation (MJO). When the MJO turns active over Indonesia and the Philippines, it acts like a "weather engine," triggering widespread rising air and helping storms form in batches. This pattern lined up almost perfectly with peak typhoon season, leading to one system after another.

Large-scale circulation patterns have shifted too. The Walker circulation, the atmospheric conveyor belt along the equator, tilted toward the Northwest Pacific, again mimicking La Niña. At the same time, equatorial waves such as Kelvin and Rossby waves repeatedly disturbed the Intertropical Convergence Zone, planting the "seeds" of storms from the Philippines to the South China Sea.

And then there’s the steering system. This year, the western Pacific subtropical high spread farther south than usual. That pushed storms along its western edge, guiding them toward the Philippines and Vietnam instead of curving harmlessly into the North Pacific as they often do.

But the most powerful ingredient was heat.

Sea-surface temperatures across the South China Sea and the waters east of the Philippines were 1–1.5 C above average in October and November, a massive jump in ocean-climate terms. Warm water is pure fuel for storms. It helps them form more easily, intensify more quickly and maintain their strength as they track westward.

Meteorologist Nguyen Binh Phong says climate change is now shaping these extremes in unmistakable ways. A warmer, moister atmosphere does not necessarily increase the number of storms globally, but it does supercharge how they behave: stronger winds, heavier rain, faster intensification.

That is exactly what 2025 has delivered: storms that strengthen with alarming speed, including several that reached severe intensity after only a short burst over open water.

Phong notes that this year’s exceptional season came from a perfect overlap: warm seas, favorable MJO phases and unusually stable upper-level winds, which allowed storms to form one after another.

To prepare, he says Vietnam must invest in early monitoring, combining data from JTWC, JMA, Digital Typhoon, VNDMS and long-range climate models. Even weaker storms can unleash destructive rainfall and trigger landslides across the central region and Central Highlands, he warns.

Risk maps need updating, and local governments should plan not just for more storms, but for stronger, wetter and faster-changing ones.