South China Sea: Tropical Storm Choi-Wan tracking northward off northwestern Luzon, Philippines, June 3 /update 6

Event

Tropical Storm (TS) Choi-Wan (known in the Philippines as Dante) is tracking northward over the South China Sea off northwestern Luzon, Philippines, June 3. As of 11:00 CST, the storm's center of circulation was approximately 1,002 km (623 miles) south-southwest of Taipei, Taiwan. Choi-Wan is forecast to maintain its strength as it continues northward in the South China Sea, bringing severe weather and its associated impacts to the northern and western coasts and regions of Luzon through June 3. The system is forecast to turn northeasterly and weaken into a tropical depression as it makes a close approach to southern Taiwan June 4. The system will then continue northeasterly over the Ryukyu Islands, with a potential close approach to Okinawa June 6. Choi-Wan will weaken rapidly and transition into a post-tropical cyclone with tropical depression winds as it enters the northern Phillippine Sea, likely dissipating south of Honshu, Japan, June 8. Some uncertainty remains in the track and intensity forecast, and changes could occur over the coming days. As of June 3, at least three people in the Philippines have died due to flooding associated with the system.

Government Advisories
As of 11:00 PHST, Philippine authorities have issued the following warnings:

• Orange Severe General Flood Advisory: Portions of Bataan, Zambales, Pangasinan, La Union, Cavite, Quezon, Laguna, Batangas, Rizal, Occidental Mindoro, Oriental Mindoro, Palawan, Romblon, and Marinduque provinces.

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
TS Choi-Wan is forecast to bring heavy rainfall, strong winds, and rough seas to coastal areas of the northern Philippines over the coming days. Sustained heavy rainfall could trigger flooding in low-lying communities near streams, creeks, rivers, and urban areas with easily overwhelmed or a lack of stormwater drainage systems. Sites located downstream of large reservoirs could experience flash flooding after relatively short periods of intense rainfall. Flooding could isolate some communities for several days. Rain-induced landslides are possible in steeply sloped terrains. Prolonged swells and storm surge generated by the system will likely result in coastal flooding as the system tracks close to land. 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 heavy rain, flooding, and storm surge, damaging wind gusts will persist. Widespread and prolonged power outages due to uprooted trees and toppled utility lines are possible. Electricity supply disruptions have occurred in some areas, including parts of Surigao del Sur Province, due to the flooding. Lingering outages may still occur in the coming days after the storm dissipates.

Transport
In addition to the immediate threat to personal safety, inclement weather associated with the storm could trigger localized business, transport, and utility disruptions through at least June 8. 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 airports.

Disruptions triggered by inclement weather and resultant hazards, such as flooding, could persist well after conditions improve. 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 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 storm 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 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. Keep any necessary medications in a waterproof container.

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
Japan Meteorological Agency
Central Weather Bureau, Taiwan