Typhoon Dujuan brushed past Tokyo and battered eastern Japan on 21 September 2026 with record rainfall and violent winds. The storm triggered severe flooding and landslides across Chiba, Kanagawa and the Tokyo area, leaving at least four people dead, six missing and more than 45,000 households without power. The event has renewed focus on Japan flood warnings, typhoon tracking and disaster response during the peak typhoon season.
What Is a Typhoon
A typhoon is a mature tropical cyclone that forms over the northwestern Pacific Ocean with sustained winds of at least 119 kilometres per hour. It is a rotating low pressure system powered by heat and moisture from warm ocean water. Typhoons bring violent winds, torrential rain, flooding, landslides and storm surges across East Asia.
A tropical cyclone is the scientific name for a rotating storm that develops over warm tropical oceans. The same type of storm gets different names in different ocean basins. This naming difference often confuses readers, but the physics remains identical.
| Storm Name | Ocean Basin | Area Covered |
|---|---|---|
| Typhoon | Northwestern Pacific Ocean | Japan, Philippines, China, Taiwan, Vietnam, Korea |
| Hurricane | Atlantic Ocean and Eastern North Pacific | Americas, Caribbean |
| Cyclone | Indian Ocean and South Pacific | India, Bangladesh, Australia |
The Japan Meteorological Agency (JMA), the national weather authority of Japan, classifies western Pacific storms by sustained wind speed. A tropical depression has winds below 63 kilometres per hour. A tropical storm has winds from 63 to 88 kilometres per hour. A severe tropical storm has winds from 89 to 117 kilometres per hour. A system becomes a typhoon once winds reach 119 kilometres per hour or more. The most intense systems, with winds above 241 kilometres per hour, are called super typhoons by the United States Joint Typhoon Warning Center.
How Typhoons Form and Why They Happen
Typhoons form through a process called tropical cyclogenesis, which means the birth of a tropical storm. The process starts when sea surface temperature rises above 26.5 degrees Celsius to a depth of about 50 metres. Warm water evaporates rapidly and pumps huge amounts of heat and moisture into the air above. This heat acts as fuel for the storm.
As warm moist air rises, it cools and condenses into towering thunderstorm clouds. Condensation releases latent heat, which warms the surrounding air further and makes it rise faster. This creates a zone of low pressure near the ocean surface, and surrounding air flows inward to fill it. The Coriolis effect, which is the bending of moving air caused by the rotation of the Earth, then curves this inflowing air into a spin. Typhoons rarely form within five degrees of the equator because the Coriolis effect is too weak there to start rotation.
Two more conditions decide whether the spin grows or dies. The air must remain humid through a deep layer so that thunderstorms do not dry out. Vertical wind shear, which means the change in wind speed and direction with height, must stay low. Strong shear tears the top off the developing storm and stops it from organising. When warm water, moist air, low shear and sufficient spin come together, a cluster of thunderstorms organises into a depression, then a tropical storm and finally a typhoon with a calm central eye surrounded by a violent eyewall.
Typhoons are dangerous natural disasters because they combine several hazards at once. The eyewall packs the strongest winds that damage buildings, snap power lines and uproot trees. Spiral rainbands dump intense rain for hours, which swells rivers and floods cities. In coastal and hilly areas, this rain triggers landslides and flash floods. A typhoon weakens after landfall or after moving over cooler water because it loses its supply of warm moist air. Many storms that reach Japan later change into extratropical cyclones, which are storms that draw energy from temperature contrasts in the atmosphere rather than from warm oceans.
When Is Typhoon Season in Japan
Typhoon season in Japan runs from May to October, with peak activity in August and September. September records the highest number of landfalls on Japan, with an average of 1.0 landfall per year. August follows closely with 0.9 landfalls, while July and October bring fewer direct hits.
The northwestern Pacific is the most active tropical cyclone basin in the world. About 25 to 30 named storms form in this basin every year. Of these, around 12 approach Japan and only about 3 make landfall in an average year. Eastern Japan, which includes the Kanto region around Tokyo, Chiba and Kanagawa, often faces heavy rain even when a typhoon does not make direct landfall. Moist air flowing around the storm, combined with seasonal rain fronts, can saturate soils days before the centre arrives.
Dujuan struck exactly in this peak window. The Japan Meteorological Agency had warned that late September storms carry a high flood risk because rivers are already full and soils are already wet from summer rains. That background explains why rainfall totals climbed to record levels even as Dujuan began to weaken and move northeast into the Pacific.
How Typhoons Are Named and Tracked in Japan
Typhoons in the western Pacific receive names from a rotating list maintained by the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center. The RSMC Tokyo Typhoon Center operates inside the Japan Meteorological Agency under the framework of the World Meteorological Organization (WMO), the United Nations agency for weather and climate. Fourteen countries and territories in the region each contribute names drawn from animals, flowers, trees, natural phenomena and cultural symbols. The name Dujuan was contributed by China and means a type of azalea flower. Particularly deadly or destructive names are retired from the list out of respect for affected communities and replaced with new names.
Tracking relies on a layered system run by the Japan Meteorological Agency. The Japan Meteorological Agency began in 1875 as the Tokyo Meteorological Observatory and took its present name in 1956. The agency is headquartered in Toranomon, Minato City, Tokyo and functions under the Ministry of Land, Infrastructure, Transport and Tourism. The RSMC Tokyo Typhoon Center was set up within the agency in 1989 to issue positions, movement, central pressure and wind forecasts for every tropical storm in the western North Pacific and South China Sea.
A typhoon forecast combines data from weather satellites, land based Doppler radar, ocean buoys, automated weather stations and computer models. Satellites watch cloud patterns and sea surface temperature continuously. Doppler radar measures rainfall intensity and wind near the coast. Buoys record wave height, pressure and wind over the open ocean. Numerical weather prediction models then simulate the track, intensity, rainfall and storm surge risk up to 120 hours ahead. The Japan Meteorological Agency updates its tropical cyclone information every three hours, and every hour when a storm comes within 300 kilometres of Japan.
A typhoon warning in Japan uses a five level alert scale for heavy rain, floods, landslides and storm surges. Level 2 asks residents to check evacuation routes. Level 3 asks elderly people and others who need more time to start evacuating. Level 4 asks all residents in danger zones to evacuate. Level 5 signals a life threatening situation and calls for immediate safety action. A typhoon tracker shown on maps displays the present centre, forecast circle, 50 knot and 30 knot wind areas and storm warning zones. During Dujuan, the Japan Meteorological Agency issued heavy rain, flood, landslide and storm surge warnings for the Kanto region and used live risk maps for floods and landslides to guide local evacuation advisories.
Typhoon Dujuan Impact on Eastern Japan
Typhoon Dujuan approached the Pacific coast of eastern Japan on 21 September 2026 and brushed past Tokyo overnight before moving out into the Pacific by the morning of 22 September 2026. The Japan Meteorological Agency warned of torrential rain, violent winds and high risk of landslides across the Kanto region. Even as Dujuan weakened into an extratropical system, its broad rainbands kept dumping water over Tokyo, Chiba and Kanagawa.
Record Rainfall in the Tokyo Area
Dujuan produced record breaking precipitation across the Tokyo region. Oshima Island, located about 120 kilometres south of central Tokyo, recorded 832 millimetres of rain in 48 hours. That total was more than double the average rainfall for the whole month of September. Edogawa Ward in eastern Tokyo recorded 282.5 millimetres in 24 hours, a new local record.
| Location | Rainfall Record | Context |
|---|---|---|
| Oshima Island | 832 mm in 48 hours | More than double the September monthly average |
| Edogawa Ward, Tokyo | 282.5 mm in 24 hours | Local record for 24 hour rainfall |
| Eastern Japan coast | Repeated bands of torrential rain on 21 September 2026 | Triggered river rises and urban waterlogging |
This intense burst matters because slow moving rainbands can cause more flooding than wind alone. Streets in Ichikawa and Funabashi in Chiba Prefecture went under water. Roads near Kamakura Station in Kanagawa Prefecture flooded, and city authorities warned that driving was dangerous. Flood water also entered parts of low lying neighbourhoods east of Tokyo.
Flooding and Landslides Across Chiba and Kanagawa
Heavy rain saturated hillsides and triggered multiple landslides in Chiba Prefecture and Kanagawa Prefecture, both part of the densely populated Kanto plain near Tokyo Bay. A landslide in Kamogawa in Chiba buried homes and forced overnight search operations. Flood alerts remained in place for rivers and low lying districts while rescue teams checked damaged houses.
The Fire and Disaster Management Agency reported that more than 460 houses were damaged. Search operations continued for six people missing after landslides. The physical pattern was typical of typhoon induced landslides. Prolonged rain loosens soil on steep slopes, and a final intense spell sets the slope moving. In cities, concrete surfaces prevent water from soaking in, so drains overflow and streets turn into channels.
Deaths, Power Cuts and Transport Disruption
Authorities confirmed at least four deaths, with three in Chiba Prefecture and one in Kanagawa Prefecture, along with 22 people injured. The toll later rose in local tallies as rescuers reached isolated areas, which shows why early figures in fast moving disasters often change within a day. More than 45,000 households in Chiba remained without electricity on the afternoon of 22 September 2026 after winds brought down lines and poles.
Evacuation pressure was large. More than 1.6 million people in and around Tokyo received evacuation advisories, while more than 74,000 people in the Tokyo region remained under stricter evacuation orders at the peak. Advisories urge people to leave danger zones but are not compulsory orders.
Transport came to a near halt. Japan Airlines cancelled 135 flights and All Nippon Airways cancelled 140 flights, taking the total above 275 flights on 21 September 2026, with wider disruption touching up to 500 domestic and international services at Tokyo airports. The Tokyo Game Show, one of the largest video game trade fairs in the world, closed early on its final day. An outdoor music festival and a baseball match scheduled in Chiba were also cancelled. Rail and road links faced delays and closures due to flooding and fallen debris.
Why Eastern Japan Faces Severe Flooding and Landslide Risk
Eastern Japan combines dense cities, steep hills and a long Pacific coastline, which magnifies typhoon damage. The Kanto plain holds Tokyo, Yokohama, Chiba and surrounding cities around Tokyo Bay. Millions live on low lying land crossed by short, fast flowing rivers. When record rainfall arrives in a few hours, rivers rise quickly and urban drains overflow. Coastal winds can also push sea water onshore and worsen flooding at river mouths.
Chiba and Kanagawa add landslide risk to this flood risk. Both prefectures have hilly districts where homes sit close to slopes. Long rain softens volcanic and sedimentary soils common in the region. Narrow valleys then funnel water and debris into settlements. That is why the Japan Meteorological Agency pairs heavy rain warnings with separate landslide risk maps rather than treating rain alone as the danger.
A warmer atmosphere holds more water vapour, so typhoons can now release heavier downpours than in the past. Scientists link human driven climate change to this rise in rainfall intensity. Rising sea levels also allow storm driven water to reach further inland. For Japan, this means that even a weakening typhoon like Dujuan can still produce record precipitation and severe urban flooding.
The Way Forward
By the morning of 22 September 2026, Dujuan had moved away from the Japanese coast and the Japan Meteorological Agency lifted or downgraded most heavy rain and landslide warnings. Local governments kept search teams in the field for missing persons and started damage surveys of homes, roads and power networks. Power companies worked to restore supply to households in Chiba while railway and airport operators cleared backlogs.
The response points to three practical lessons. Early evacuation advisories for more than a million people helped limit casualties despite record rain. Live flood and landslide risk maps allowed cities to target the most danger prone wards rather than shutting entire regions. Rapid flight cancellations and event closures reduced the number of people caught outdoors during violent winds. Authorities are expected to review drainage capacity in Edogawa and other low lying wards, slope protection in landslide hit districts and backup power for storm prone feeders before the next peak of the Pacific typhoon season.
Key Takeaways
- Typhoon Dujuan struck eastern Japan on 21 September 2026 and moved into the Pacific by the morning of 22 September 2026.
- Oshima Island recorded 832 mm of rain in 48 hours, while Edogawa Ward in Tokyo recorded 282.5 mm in 24 hours.
- The storm caused at least four deaths, six missing persons, 22 injuries and left over 45,000 households in Chiba without power.
- A typhoon is a tropical cyclone of the northwestern Pacific with sustained winds of at least 119 kilometres per hour.
- The Japan Meteorological Agency, established in 1875 and headquartered in Tokyo, houses the RSMC Tokyo Typhoon Center set up in 1989.
- Japan typhoon season runs from May to October with a peak in August and September, when about 12 storms approach Japan each year.
