South China Sea: Typhoon Rai tracking northwestward in the South China Sea; close approach to Vietnam Dec. 19 /update 12

Event

Typhoon Rai (known locally in the Philippines as Odette) is tracking northwestward across the South China Sea as of Dec. 19. As of 16:00 ICT, the storm's center of circulation was approximately 340 km (212 miles) southeast of Da Nang, Vietnam. Forecast models indicate the system will weaken as it turns to track northward along the Central Vietnam coast through Dec. 19 and make a close approach to the Paracel Islands early Dec. 20. The storm will weaken rapidly into a tropical storm as it turns northeastward and passes southeast of Hainan Province, China Dec. 20. Rai is then forecast to further weaken into a tropical depression as it turns to track east-northeast along the southern coast of mainland China through Dec. 21 and towards southern Taiwan through early Dec. 22. No further landfalls are forecast. Some uncertainty remains in the track and intensity forecast, and changes could occur over the next few days.

Authorities in the Philippines have evacuated at least 376,000 people across the Caraga, Central Visayas, Eastern Visayas, Northern Mindanao, Mimaropa, Western Visayas, and Zamboanga Peninsula regions. Hundreds of schools and offices have been temporarily closed in the affected areas.

As of Dec. 19, more than 100 fatalities have occurred across the Central Philippines, including at least 63 people in Bohol, 22 in Negros Oriental, 10 in Dinagat Islands, and 18 in Surigao del Norte provinces. The casualty numbers will likely increase in the coming days. Reports indicate substantial infrastructure damage in Surigao City, northern Mindanao; landslides, fallen trees, and power lines have cut off roads to the city. Reports also indicate flooding in Cagayan de Oro, Bohol, and Kabankalan, among other locations. A storm surge of 5 meters (16.5 feet) destroyed at least 4,000 houses in Sogod, Southern Leyte.

Authorities are working to restore power in many regions; however, outages are ongoing in Bohol Province as of Dec. 19, with partial outages in Agusan del Norte, Agusan del Sur, Cebu, Eastern Samar, Leyte, Negros Occidental, Negros Oriental, Northern Samar, Samar, Southern Leyte, Surigao del Norte, and Surigao del Sur. Bohol and Cebu provinces have declared a state of calamity. Additional details on the situation will likely emerge in the coming days as authorities conduct thorough damage assessments.

Government Advisories
As of Dec. 19, Vietnamese officials have warned of moderate-to-heavy rain of 4-8 cm (1.5-3 inches) from Thua Thien Hue to Phu Yen provinces through Dec. 19. Strong winds are forecast across Quang Ngai, Binh Dinh, Phu Yen Thua Thien Hue, Da Nang, and Quang Nam provinces. The rivers in Quang Nam to Khanh Hoa provinces are in danger of flooding, especially the Song Ky Lo and Ba rivers in Phu Yen Province and the rivers in Quang Ngai, Binh Dinh, Khanh Hoa, and Quang Nam provinces. There is a high risk of flash floods, landslides in mountainous areas, and flooding in low-lying and riverside areas.

The China Meteorological Administration has issued a blue (lowest level on a four-tier scale) typhoon warning, warning of heavy rain of 4-8 cm (1.5-3 inches) over eastern Hainan Island through the afternoon of Dec. 20.

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
Typhoon Rai will likely continue to bring heavy rainfall, strong winds, and rough seas to western parts of the Philippines 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. Tugdan Airport (TBH) in Romblon Province was closed Dec. 15, and operations remain suspended at Puerto Princesa International Airport (PPS) as of Dec. 19. The Sayak Airport (IAO) terminal in Siargao has sustained damages; however, the runway is clear of debris, and planes carrying relief goods can land. Officials plan to reopen Mactan-Cebu International Airport (CEB) Dec. 19, with limited domestic flights operating.

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
Philippine Atmospheric, Geophysical and Astronomical Services Administration
China Meteorological Administration
Vietnam National Center for Hydrometeorological Forecasting (Vietnamese)