Why Are Autumn Typhoons More Ferocious? The Mystery Behind the Peak Season for Super Typhoons in September–November
Key SummaryMany people assume that once the Start of Autumn has passed and September and October arrive, major typhoons are no longer likely. However, meteorological statistics show that China’s strongest landfalling typhoons — "RAMMASUN," "MANGKHUT," "YAGI," and "MUJIGAE" — have almost all been autumn typhoons! Why are autumn typhoons so devastating?
The Big Data Truth: September Is the "Peak Throne" for Super Typhoons
In meteorology, typhoons that form from June through August are generally called "summer typhoons," while those that form from September through November are called "autumn typhoons." Although the greatest number of typhoons forms in August, September and October have the highest average intensity and the largest proportion of super typhoons!
| Dimension | Summer Typhoons (June–August) | Autumn Typhoons (September–November) |
|---|---|---|
| Number Formed | The most (about 45% of the annual total) | Slightly fewer than in summer (about 38% of the annual total), but with an exceptionally high rate of major typhoons |
| Sea Surface Temperature and Energy | The ocean is still heating up, with a relatively shallow layer of warm water | After being heated throughout midsummer, the warm-water layers in the western North Pacific and South China Sea are at their deepest, with energy reserves peaking for the year |
| Main Landfall Areas | Across southern China, Taiwan, Fujian and Zhejiang, Jiangsu and Shanghai, and even northern China | As the subtropical high retreats southward, they focus their attacks on Guangdong, Hainan, Taiwan, and Guangxi |
| Deadliest Weapon | Their own violent winds, heavy rain, and storm surge | Typhoon circulation + southward-moving cold air = extreme inverted-trough rainstorms and a multiplying effect on wind intensity |
Why Are Autumn Typhoons So Difficult to Defend Against? Three Deadly Characteristics
- Deep Warm Water Powers "Explosive Intensification": From September to October, sea-surface temperatures in the western North Pacific and South China Sea remain as high as 28–29°C, while warm water above 26°C extends to depths of 100 meters. As a typhoon moves through these waters, it is unlikely to weaken itself by drawing up cold water from below, making it highly prone to rapid intensification (RI) near the coast, as seen with super typhoon "MUJIGAE" in October 2015 and super typhoon "YAGI" in September 2024.
- Encountering Cold Air: A Devastating Combination of Physics and Magic: In autumn, cold air from the north begins moving south more frequently. When the typhoon’s outer warm, moist jet meets the cold air, the cold air acts like a wedge, forcing the warm, moist air to rise violently. Rainfall efficiency can be several times higher than in a typical summer typhoon. At the same time, the pressure gradient intensifies, allowing strong northerly winds to persist for longer.
- Complex Steering Flows Produce Unusual and Changeable Tracks: In autumn, the subtropical high gradually retreats eastward and southward, while the westerly trough becomes increasingly active. Within a saddle-shaped circulation pattern, typhoons are prone to stalling and looping near the coast, making sharp right-angle turns, or following serpentine tracks, making their paths extremely difficult to forecast.