South China Sea: Tropical Depression 22W forms, tracking northwestwards Oct. 7; landfall forecast in Hainan Province, China, Oct. 8

Event

Tropical Depression 22W has formed and is tracking northwest in the South China Sea Oct. 7. As of 17:00 CST, the storm's center of circulation was approximately 689 km (428 miles) southeast of Hanoi, Vietnam. Forecast models indicate the system will strengthen into a tropical storm as it turns to track north-northwest and makes landfall over southeastern Hainan Province, China, east of Sanya City the afternoon of Oct. 8. Following landfall, the system will likely weaken as it turns to tracks northwest over Hainan Province, China before exiting into the Gulf of Tonkin the afternoon of Oct. 9. The storm is forecast to weaken further into a tropical depression as it tracks west across the Gulf of Tonkin through early Oct. 10 before tracking southwest and making landfall over Ha Tinh Province, Vietnam late Oct. 10, dissipating over Khammouane Province, Laos early Oct. 11. The storm's track and intensity forecast remain somewhat uncertain, and the system may change accordingly over the coming days.

Government Advisories
Vietnamese officials have warned of heavy rainfall of 15-25 cm (6-10 inches) from Quang Binh to Quang Ngai provinces and 5-10 cm (2-4 inches) of rainfall over Ha Tinh and Binh Dinh provinces as well as the northern Central Highlands Region through Oct. 8. The heavy rain will extend into the North Central Coast, Red River Delta, and Northeast regions Oct. 9-12.

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 to coastal areas of central Vietnam and far southern China in the coming days. Sustained heavy rainfall in central Vietnam, far southern China, central and southern Laos, and far eastern Thailand could trigger flooding in low-lying communities near streams, creeks, rivers, and urban areas with inadequate 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 as the system approaches land. 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.

Disruptions triggered by inclement weather and resultant hazards, such as flooding, could persist well after 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 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
China Meteorological Administration
Vietnam National Centre for Hydro-Meteorological Forecasting (Vietnamese)