Japan: Tropical Storm Chanthu tracks eastward in Seto Inland Sea after landfall in Nagasaki Prefecture late Sept. 17 /update 7

Event

Tropical Storm Chanthu has weakened slightly while tracking eastward in the Seto Inland Sea late Sept. 17. As of 21:00 JST, the storm's center of circulation was approximately 78 km (48 miles) southwest of Iwakuni, Japan. The system made an initial landfall in Fukuoka Prefecture earlier on Sept. 17. Chanthu is forecast to move in an east-northeasterly course, making multiple additional landfalls over western and southern Japan as a tropical storm - particularly in Ehime, Kagawa, and Wakayama prefectures - through Sept. 18. The storm is then forecast to weaken into a tropical depression and begin tracking eastward, and then southeastward, near the coast of Shizuoka and Chiba prefectures late Sept. 18 through early Sept. 19. Chanthu will subsequently dissipate southeast of Chiba late Sept. 19. The storm's track and intensity forecast remain uncertain, and the system may change accordingly over the coming days.

Officials in South Korea have evacuated residents from landslide-prone areas in South Jeolla Province. Japanese officials have also ordered evacuations in parts of Kochi, Nagasaki, and Kumamoto prefectures. Additional evacuations are possible.

Government Advisories
As of late Sept. 17, the Japan Meteorological Agency has issued the following warnings:

• Red (middle level on a three-tier scale) warnings for severe weather are in place in parts of Ehime, Kochi, Tokushima, Yamaguchi, Kagawa, Wakayama, Oita, Mie, and Hyogo prefectures.

• Yellow advisories for potentially hazardous winds, landslides, heavy rain, and thunderstorms are in place for the rest of the affected area throughout central and southern Japan.

Heavy rain and strong winds are forecast over parts of Japan with rainfall of up to 30 cm (12 inches) over the Shikoku Region, 25 cm (10 inches) over the Tokai Region, 20 cm (8 inches) over the Kinki and Kanto regions, 18 cm (7 inches) over the Chugoku Region, 15 cm (6 inches) over the Kyushu, Tohoku, and Hokkaido regions, and 12 cm (4.5 inches) over the Hokuriku Region through the morning of Sept. 18.

Authorities will likely issue new warnings or update existing advisories throughout the system's progression in the coming days. Weather warnings could remain active even after the system's immediate threat has diminished, as some areas may still be highly susceptible to rain-induced hazards. The possibility of localized evacuations cannot be discounted if weather conditions prove particularly hazardous.

Hazardous Conditions
The storm may bring heavy rainfall, strong winds, and rough seas over the coming days to parts of southeastern South Korea and most of central and southern Japan. Sustained heavy rainfall could trigger flooding in low-lying communities near streams, creeks, rivers, and urban areas with easily overwhelmed or a lack of stormwater drainage systems.

Sites located downstream of large reservoirs could experience flash flooding after relatively short periods of intense rainfall. Rain-induced landslides are possible in steeply sloped terrains. Flooding could isolate some communities for several days. Prolonged swells and storm surge generated by the system will likely result in coastal flooding. Persistent onshore flow could make it difficult for the surge to recede and for water levels to decrease in coastal river catchments.

Transport
Inclement weather associated with the storm could trigger localized business, transport, and utility disruptions. Floodwaters and debris flows could render some bridges or roadways impassable, impacting overland travel in and around affected areas. Areal flooding in urban locations could also result in severe traffic congestion, while strong winds will pose a hazard to high-profile vehicles. Heavy rain and low visibility may trigger flight disruptions at regional airports.

Chanthu has prompted South Korean officials to suspend some ferry services in Jeju Province and parts of South Jeolla Province Sept. 17. Authorities also canceled several flights at Jeju International Airport (CJU).

Officials at JR West in Japan have suspended multiple passenger train services in western Japan. Officials will likely update information on train services as the conditions change. Ferry services connecting Yawatahama, Ehime Prefecture with Oita, Matsuyama with Yanai in Yamaguchi Prefecture, and Hakata Port with Iki and Tsushima, have suspended operations as a precaution. Numerous flights from Osaka International Airport (ITM), two flights from Kansai International Airport (KIX), and all flights from Matsuyama Airport (MYJ) have been canceled. Japan Airlines and All Nippon Airways have canceled dozens of flights mainly from airports serving Kyushu. Additional flight, train, and passenger ferry cancelations or delays are likely in affected areas of southern and central Japan.

Disruptions triggered by inclement weather and resultant hazards, such as flooding could persist well after weather conditions have improved. If there is severe damage to infrastructure, repair or reconstruction efforts may exacerbate residual disruptions.

Health
Stagnant pools of water during and after flooding increase the incidence of insect- and waterborne diseases, such as dengue fever, cholera, and malaria. The threat of these disease outbreaks is usually elevated in the low-income or underdeveloped areas of major urban centers due to the presence of incomplete or open sewer lines. The latent threat of waterborne contaminants from inundated industrial sites cannot be discounted; exposure to raw sewage and other hazardous materials mixed with floodwaters poses a serious health threat.

Advice

Activate contingency plans in areas where officials forecast tropical storm conditions. Heed any evacuation orders that may be issued. Use extreme caution in low-lying coastal areas and near streams, creeks, and other waterways due to the potential for severe flooding and storm surge. Stockpile water, batteries, and other essentials in advance. Charge battery-powered devices when electricity is available; restrict the use of cellular phones to emergencies only. Power down mobile devices when not in use. Keep important documents and necessary medications in waterproof containers. Observe strict food and water precautions, as municipalities could issue boil-water advisories following flooding events. Take precautions against insect- and waterborne diseases in the coming weeks.

Plan accordingly for protracted commercial, transport, and logistics disruptions in areas in the path of the storm, especially if vital infrastructure is damaged. Seek updated information on road conditions before driving or routing shipments through areas where flooding has occurred. Confirm flights before checking out of hotels or driving to the airport; clearing passenger backlogs may take several days in some locations.

Resources

Joint Typhoon Warning Center
Japan Meteorological Agency (Japanese)
Korea Meteorological Administration (Korean)