What is the Remnant Circulation After a Typhoon Makes Landfall and Weakens? Can It Still Cause Heavy Rainstorms?
TyphoonSays·防御问答 · Typhoon knowledge · 更新 at 2026-08-09
The Typhoon "Dead but Not Gone": Understanding Remnant Circulation
After the center of a typhoon makes landfall, it loses its massive source of energy and water vapor from the ocean. Combined with the friction from the land surface, wind speeds typically weaken rapidly. According to the national standard for tropical cyclone classification by the China Meteorological Administration (CMA), when maximum wind speeds drop below Force 8, meteorological departments stop assigning it a number, meaning it is no longer classified as a "typhoon." However, this does not mean the danger has completely passed. At this stage, although the spiral cloud bands originally tightly wrapped around the typhoon's center become loose, the low-pressure system still exists and continues to move deeper inland under the guidance of atmospheric circulation. This low-pressure system, which has lost its typhoon name but retains certain rotational characteristics, is what we must be wary of as "typhoon remnant circulation." It is like an injured beast that has not yet fallen; although its claws and teeth (wind force) are no longer sharp, its bulk (water vapor and energy) remains immense.
Risk of Heavy Rainstorms May Actually Increase
Many people mistakenly believe that wind and rain will stop immediately after a typhoon makes landfall. In fact, the rainfall hazards brought by remnant circulation are often more hidden and persistent than those during the initial landfall. There are three main reasons:
- Uninterrupted Water Vapor Transport: Remnant circulation acts like a huge water pump. As long as it remains connected to the ocean or combines with other weather systems (such as monsoon troughs or cold air), it can continuously draw large amounts of water vapor from the sea and transport it inland.
- Orographic Lifting Effect: When remnant circulation encounters mountain ranges inland, the airflow is forced to rise, cool, and condense, easily forming high-intensity orographic rain. This rainfall is often concentrated in mountainous areas or on windward slopes, resulting in astonishing precipitation amounts.
- Slower Movement Speed: Low-pressure systems after landfall usually move slowly, and may even stagnate in certain areas. This means the same region will suffer from prolonged rainfall, easily leading to cumulative disasters.
Therefore, even if wind speeds decrease, red warnings for heavy rainstorms may still remain in effect. Please note that standards for school suspensions and work stoppages corresponding to heavy rain warnings may vary by location; please refer to announcements from local governments.
Shift Focus from "Wind Protection" to "Flood Prevention"
Facing remnant circulation, our defense strategies need to be adjusted promptly. The primary threat at this stage is no longer strong winds capable of toppling trees or billboards, but secondary disasters caused by persistent heavy rainstorms. Residents should focus on the following points:
- Beware of Flash Floods and Geological Disasters: Residents living in mountainous areas, river valleys, or areas prone to geological hazards must closely monitor risk alerts issued by local natural resources departments. Even if the rain seems light, landslides and debris flows are highly likely once soil saturation is reached.
- Prevent Urban Waterlogging: Heavy rainfall may overload urban drainage systems, causing water accumulation in low-lying areas, underground garages, and subway entrances. When traveling, avoid vortex-like water flows and stay away from utility poles and transformers.
- Do Not Rush to Return or Go Out: Do not rashly visit seaside or mountainous areas for leisure just because the wind has weakened before meteorological departments lift relevant warnings. The impact range of remnant circulation can cover hundreds of kilometers, affecting multiple provinces.
Disaster prevention and mitigation is a protracted battle; do not let your guard down just because the typhoon has been "renamed." Real-time typhoon tracks can be queried at TyphoonSays (taifengshuo.com)
This article is typhoonsay's original copy content, and the local policy standards are based on the local government's latest release.