Gulf of Tonkin: TS Lionrock tracking west-northwestwards over Gulf of Tonkin early Oct. 10. Landfall forecast in Thanh Hoa Province, Vietnam, early Oct. 11 /update 4

Event

Tropical Storm Lionrock (formerly 22W) is tracking west-northwest over the Gulf of Tonkin early Oct. 10 after landfall over Qionghai, Hainan Province, China, late Oct. 8. As of 05:00 CST, the storm's center of circulation was approximately 304 km (189 miles) east-southeast of Hanoi, Vietnam.

Forecast models indicate the system will strengthen briefly before weakening again as it turns to track west-southwest in the Gulf of Tonkin, making landfall as a tropical storm over Thanh Hoa Province, Vietnam, early Oct. 11. Lionrock is likely to track southwestwards across Nghe An Province in Vietnam through the afternoon of Oct. 11 before tracking across Bolikhamsai Province in Laos, Bueng Kan Province in Thailand, and dissipating over Sakon Nakhon Province in Thailand early Oct. 12. The storm's track and intensity forecast remain somewhat uncertain, and the system may change accordingly over the coming days.

Reports indicate that one person died and 13 others were injured in Hong Kong.

Government Advisories
Chinese officials maintain a blue typhoon warning (the lowest on a four-tier scale) as of early Oct. 10. Heavy rains are also forecast for western Guangdong, western and southern Guangxi, southern and northern Guizhou, western Hainan Island, and southeastern Yunnan provinces through early Oct. 11. The heaviest rainfall is likely to occur over southern Guangxi, with 10-16 cm (4-6 inches) of rainfall forecast.

Vietnamese officials have warned of heavy to very heavy rainfall of 15-20 cm (6-8 inches) across the Northeast Region and heavy rainfall of 5-10 cm (2-4 inches) across the Northwest Region through Oct. 11. Heavy to very heavy rainfall of 10-25 cm (4-10 inches) is forecast over the North Central Region through Oct. 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 northern Laos, and 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.

Authorities have suspended all ferry services in the Qiongzhou Strait. Due to the storm, authorities canceled at least 219 flights from Haikou Meilan International Airport (HAK) and two flights from Macau International Airport (MFM). Haikou Xinhai Port, Xiuying Port, and Railway South Port were suspended early Oct. 9. Services are likely to resume from early Oct. 10.

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
Thai Meteorological Department
Vietnam National Centre for Hydro-Meteorological Forecasting (Vietnamese)