South China Sea: Tropical Depression Conson tracks northwestward off the coast of central Vietnam early Sept. 13 /update 4

Event

Tropical Depression Conson is tracking northwestward in the western South China Sea close to the coast of central Vietnam early Sept. 13. As of 01:00 ICT, the storm's center of circulation was approximately 113 km (70 miles) southeast of Da Nang. In recent days, the system has been moving slowly near Ly Son Island. However, Conson is forecast to track northwestward and make landfall over northern Quang Nam Province before midday Sept. 13. After landfall, the system will likely weaken rapidly, dissipating over eastern Savannakhet Province, Laos, the afternoon of Sept. 14.

Government Advisories
Vietnamese officials have warned of potentially hazardous weather in central parts of the country from Da Nang Municipality to the north of Quang Ngai Province through at least Sept. 13 where rainfall totals of 5-10 cm (2-4 inches) are possible. Heavy to very heavy rainfall of 10-20 cm (4-8 inches) is likely over Quang Tri to Thua Thien Hue provinces through Sept. 13 while moderate to heavy rain is forecast over Quang Binh to Thanh Hoa provinces through Sept. 14. 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 will likely bring heavy rainfall, strong winds, and rough seas to parts of central Vietnam and southern Laos through Sept. 14. Urban flooding has been reported in parts of Da Nang. Sustained heavy rainfall could trigger additional flooding in low-lying communities near streams, creeks, rivers, and urban areas with easily overwhelmed 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. Vietnamese authorities have ordered at least 330,000 residents in potentially threatened areas to evacuate as a precaution.

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.

Tornadoes are also possible over the affected area.

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. Officials may also suspend ferry and cargo services in affected areas.

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
Vietnam National Centre for Hydro-Meteorological Forecasting (Vietnamese)