Indian Ocean: Category-1 Tropical Cyclone Seroja continues to track southwestward off Nusa Tenggara region, Indonesia, as of April 7 /update 4

Event

Category-1 Tropical Cyclone Seroja continues to track southwestwards in the Indian Ocean south of Sumba Island, East Nusa Tenggara Province, Indonesia, April 7. As of 08:00 WITA, the storm's center of circulation was around 1,080 km (671 miles) north-northeast of Learmonth, Western Australia. Forecast models indicate the system will strengthen into a Category 4-Severe Tropical Cyclone and turn southwards by April 10. Seroja is forecast to shift southeastward and make landfall over the Gascoyne region in Western Australia April 11, before weakening into a Category-2 Tropical Cyclone through April 12. Significant uncertainty remains in the track and intensity forecast, and changes could occur over the coming days.

Government Advisories
Indonesia's Agency for Meteorology, Climatology, and Geophysics (BMKG) continues to warn of high waves in the Indian Ocean off East Nusa Tenggara, including south of Sumba Island, as of the morning of April 7. The agency is also advising of moderate to heavy rains and strong winds in West Nusa Tenggara, Bali, Central Java, East Java, and Yogyakarta provinces, and moderate rains in East Nusa Tenggara Province in the next 24 hours. Additionally, the Australian Bureau of Meteorology (BOM) stated that the system could approach Western Australia's Gascoyne region from April 9. Authorities will likely issue new warnings or update existing advisories 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.

Hazardous Conditions
Reports indicate numerous landslides, along with significant areal flooding, in parts of southern Indonesia following the passage of Seroja. Indonesian authorities have clarified that severe weather and related disruptions have killed at least 86 people as of April 7, with around 98 people missing. Official casualty figures are likely to rise in the coming days. Strong winds also damaged multiple structures, including roads and bridges in several communities, displacing thousands of residents as of early April 7. Additionally, officials in East Nusa Tenggara Province have reported damaged power facilities and outages in Kupang and other parts of the region.

Far western regions of Western Australia will likely experience severe weather from April 9. 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. 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 in other affected areas.

Transport
Inclement weather associated with the storm could trigger localized business, transport, and utility disruptions in the affected areas through at least April 12. Storm impacts have damaged bridges connecting districts in Flores Island, East Nusa Tenggara Province, Indonesia. 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. 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 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
Australia Bureau of Meteorology (BoM)