Indian Ocean: Category-1 TC Seroja tracks west-southwestward in the Indian Ocean April 5 /update 1

Event

Category-1 Tropical Cyclone Seroja continues to strengthen as it tracks west-southwestward in the Indiana Ocean, April 5. As of 19:00 Western Indonesian Time (WIB) April 5, the storm's center of circulation was approximately 748 km (465 miles) north of Broome, Australia. Forecast models indicate that Seroja will continue to strengthen as it track west-southwestward to Category-4 Severe Tropical Cyclone strength by April 9. The system is then projected to slightly weaken to a Category-3 Severe Tropical Cyclone by April 10 as it tracks near the western coast of Western Australia. Some uncertainty remains in the track and intensity forecast, and changes could occur over the coming days.

Government Advisories
As of April 5, Indonesia's Agency for Meteorology, Climatology, and Geophysics (BMKG) has warned waves as high as six meters in the Timor Sea between Rote and Timor islands in East Nusa Tenggara, with smaller waves possible over the Savu Sea and Sumba Strait. Authorities could issue new warnings or update existing advisories until the system dissipates. 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. Hundreds to thousands of locals in Indonesia's Flores Island have evacuated due to related flooding; officials could order additional localized evacuations if weather conditions prove particularly hazardous.

Hazardous Conditions
Tropical Cyclone Seroja will likely bring heavy rainfall and strong winds to coastal areas of Indonesia's East Nusa Tenggara through at least early April 6, while western parts of Western Australia may experience severe weather April 9-10. Sustained heavy rainfall could trigger flooding in low-lying communities near streams, creeks, and rivers, as well as in urban areas with easily overwhelmed stormwater drainage systems. A landslide occurred in Adonara Island, East Nusa Tenggara, Indonesia, April 4, and additional landslides may affect other hilly regions. 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. In addition to the heavy rain, flooding, and storm surge, Seroja will likely produce damaging wind gusts. Widespread and prolonged power outages due to uprooted trees and toppled utility lines are likely.

Officials in Indonesia and Timor-Leste reported flooding and landslides related to Seroja have led to at least 90 deaths and dozens of people missing; the casualty count will likely rise in the coming days. The conditions have also damaged multiple structures in the province.

Transport
Inclement weather associated with the storm could trigger localized business, transport, and utility disruptions in the affected areas through at least April 10. The conditions have damaged bridges connecting districts in Flores Island, East Nusa Tenggara Province, Indonesia, as of April 5. Floodwaters and debris flows may render additional 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, such as Kupang's El Tari International Airport (KOE). Disruptions caused 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.

Advice

Activate contingency plans in areas where officials forecast tropical storm conditions. Heed all evacuation orders, if issued. 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 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

Indonesian Agency for Meteorology, Climatology, and Geophysics
Indonesian Agency for Meteorology, Climatology, and Geophysics Twitter
Bureau of Meteorology (BoM)