Is It Safe After a Typhoon Makes Landfall? The "Second Strike" of Residual Circulation
A typhoon weakening after landfall does not mean the danger has passed. Residual circulation penetrating deep inland and combining with cold air can cause extreme rainstorms thousands of kilometers away. The '75·8' and '23·7' events are bloody lessons.
Are "Dead" Typhoons More Dangerous?
After making landfall, a typhoon loses its supply of moisture from the ocean, causing wind speeds to drop rapidly until it is no longer tracked. However, its residual circulation (residual vortex) still carries massive amounts of moisture. As it penetrates deep inland, it can deliver a "second strike."
Two Historic Rainstorm Events Caused by Residual Vortices
Henan "75·8" Extreme Rainstorm (1975)
After Typhoon Nina (7503) made landfall, it moved northward, and its residual vortex stalled over Henan Province. The intrusion of cold air combined with the residual vortex, resulting in 1,060.3 mm of rainfall in Linzhuang within 24 hours. The failure of the Banqiao and Shimantan dams caused tens of thousands of casualties, marking one of the most devastating flood disasters in the history of the People's Republic of China.
Hai River Basin "23·7" Regional Extreme Flood (2023)
After Typhoon DOKSURI made landfall in Fujian, its residual vortex moved north. Interacting with topography and cold air at the foot of the Taihang Mountains, it triggered historically rare extreme rainstorms in Beijing, Tianjin, and Hebei. Licheng County in Hebei recorded cumulative rainfall of 1,003 mm, leading to severe regional flooding across the Hai River Basin.
Separated by 48 years, these two disasters share a strikingly similar mechanism: Residual Vortex + Cold Air + Topographic Lifting.
Three Characteristics of Rainstorms from Residual Vortices
- Far from Landfall Point: They can penetrate 1,000–2,000 km inland. Affected areas often lack any "typhoon feel," leading to weak defensive awareness.
- Delayed Impact: Heavy rain occurs 2–4 days after landfall, by which time public attention has shifted away from the typhoon.
- Extremity: The precipitation efficiency from the convergence of cold and warm air masses can exceed that of the typhoon itself.
Protection Tips for Inland Residents
- After a typhoon makes landfall, if forecasts indicate its residual circulation is moving toward your area, prepare for it as an "unnamed extreme rainstorm."
- Pay attention to river flood and reservoir dispatch information from water resources departments, not just meteorological warnings.
- Plains at the foot of mountains (such as the eastern foothills of the Taihang Mountains and the northern foothills of the Funiu Mountains) are high-risk zones for rainstorms caused by residual vortices.
TyphoonSays' typhoon detail pages retain complete track records for each typhoon (including the last position before tracking ceased), which, when combined with news daily reports, allows you to track the movement of residual vortices.