Philippine Sea: Super Typhoon Chanthu tracking northwestward over the Luzon Strait as of early Sept. 11 /update 4

Event

Super Typhoon Chanthu (known in the Philippines as Kiko) is tracking northwestward over the Luzon Strait early Sept. 11. As of 23:00 PHT Sept. 10, the storm's center of circulation was approximately 494 km (306 miles) north-northeast of Manila, Philippines. Forecast models indicate the system will weaken slightly to a typhoon as it turns northward in the Luzon Strait and traverses the Babuyan and Batanes islands Sept. 11.

The storm is forecast to make landfall on Orchid Island, Taitung County, Taiwan, overnight Sept. 11-12. Chanthu is likely to weaken further as it tracks northward off the eastern coast of Taiwan and enters the East China Sea late Sept. 12. Models indicate the system will continue to lose strength as it tracks northward off the shores of Fujian and Zhejiang provinces, China, through late Sept. 13. Chanthu will turn northeastward Sept. 14 and eastward Sept. 15 in the East China Sea as it weakens to a tropical storm. The storm's track and intensity forecast remain uncertain, and the system may change accordingly over the coming days.

Government Advisories
Philippine officials forecast heavy-to-intense rainfall in Cagayan, including the Babuyan Islands, Batanes, and northern Isabela, while moderate-to-heavy rain is forecast for Ilocos Region, Cordillera Administrative Region, north and central Aurora, and the rest of Cagayan Valley through the evening of Sept. 11. Chanthu is likely to enhance the Southwest Monsoon, bringing monsoon rain over western portions of southern Luzon and Western Visayas through early Sept. 11.

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) has issued the following advisories associated with Chanthu:

• Tropical Cyclone Wind Signal (TCWS) 4*: Batanes and the northeastern Babuyan Islands

• Tropical Cyclone Wind Signal (TCWS) 3**: Extreme northeastern Cagayan and the rest of the Babuyan Islands

• TCWS 2***: Northern, central, and eastern mainland Cagayan, northeastern Isabela, and northern Apayao

• TCWS 1****: The rest of mainland Cagayan, northern Ilocos Norte, the rest of Apayao, northern Kalinga, eastern Mountain Province, northeastern Abra, northwestern and southeastern Isabela

*TCWS 4 indicates destructive typhoon-force winds are prevailing or expected within 12 hours and may cause heavy damage to structures and vegetation.
**TCWS 3 means that destructive typhoon-force winds are prevailing or expected within 18 hours and may cause moderate-to-heavy damage to structures and vegetation.
***TCWS 2 means that damaging gale-force winds are prevailing or expected within 24 hours.
****TCWS 1 means that strong winds are prevailing or expected within 36 hours.

The Central Weather Bureau in Taiwan has issued a typhoon warning for Kaohsiung City, Pingtung County, and Taitung County as of late Sept. 10. 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 coastal areas of the far northern Philippines and Taiwan 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. 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. 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.

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 or typhoon 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
Philippine Atmospheric, Geophysical and Astronomical Services Administration
Taiwan Central Weather Bureau
China Meteorological Administration (Mandarin)
Japan Meteorological Agency (Japanese)