South China Sea: Tropical Depression Rai tracking northeastward in the South China Sea Dec. 20 /update 14

Event

Tropical Depression Rai is tracking northeastward across the South China Sea Dec. 20. As of 20:00 CST, the storm's center of circulation was approximately 427 km (265 miles) south-southwest of Hong Kong, China. Forecast models indicate the system will continue to weaken in the coming hours as it passes around 200 km (124 miles) south of Hong Kong Dec. 21. Rai is then forecast to dissipate off the coast of Guangdong Province, China, late Dec. 21. No further landfalls are forecast. Some uncertainty remains in the track and intensity forecast, and changes could occur over the next few days.

Rai (known locally in the Philippines as Odette) made multiple landfalls over the central Philippines Dec. 16-17 after hitting the country as a super typhoon, causing much damage and at least 375 fatalities. Rescue and recovery efforts are underway.

Government Advisories
As of late Dec. 20, the China Meteorological Administration has issued a blue (lowest level on a four-tier scale) typhoon warning, indicating heavy rain of 5-7 cm (2-2.5 inches) over eastern and southern Fujian, eastern and central Guangxi, and northeastern Hainan provinces through late Dec. 21. Strong winds are also expected in the seas off the southern coast. The Hong Kong Observatory has issued a Standby Signal, No.1, and has advised the public to stay away from the shoreline.

Authorities will probably 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. Officials may announce additional evacuations if weather conditions prove particularly hazardous.

Hazardous Conditions
Tropical Depression Rai will likely continue to bring heavy rainfall, strong winds, and rough seas to far southern China in the coming hours. Sustained heavy rainfall could trigger flooding in low-lying communities near streams, creeks, rivers, and in 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. Prolonged sea swells and storm surge generated by the system could 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.

In addition to the forecast of heavy rain, flooding, and storm surge, the storm could produce damaging wind gusts. Widespread and prolonged power outages due to uprooted trees and toppled utility lines are possible.

Transport
Inclement weather associated with the storm could trigger localized business, transport, and utility disruptions. Floodwaters and debris flows may render some bridges, rail networks, 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 weather conditions have improved. If there is severe damage to infrastructure, repair or reconstruction efforts may exacerbate residual disruptions.

Advice

Activate contingency plans in areas where officials forecast tropical storm or typhoon conditions. Heed all evacuation orders. Use extreme caution in low-lying coastal areas and near streams, creeks, and other waterways due to the high 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 any 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

Hong Kong Observatory