Koro Sea: Tropical Cyclone Yasa weakens further into Category 1 and tracks southwestward in Koro Sea as of Dec. 19 /update 11

Event

Tropical Cyclone Yasa has further weakened into category 1 as it tracks southwestward in the South Pacific Ocean, afternoon Dec. 19, following landfall over Vanua Levu, Fiji, Dec. 17. As of 1300 FJT, the storm's center of circulation was approximately 472 km (293 miles) southeast of Suva, Fiji. Forecast models indicate that the storm will continue to weaken and track southwestward, Dec. 20. Although Yasa will not make a subsequent landfall, further impacts of the system across Fiji and southern Tonga, including Tongatapu and 'Eua, will likely continue through at least Dec. 21. Some uncertainty remains in the track and intensity forecast, and changes could occur in the coming days.

Government Advisories
A disaster declaration remains in effect across Fiji through Jan. 16, 2021. Flash floods are possible in low-lying areas, including the eastern half of Viti Levu. Gale and strong wind warnings also remain active nationwide. Officials in Tonga have issued heavy rain, gale and heavy damaging swell warnings in parts of the country through Dec. 20. Authorities will likely 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
Tropical Cyclone Yasa will likely continue to bring heavy rainfall, strong winds, and rough seas to southern Fiji and the islands of 'Eua and Tongatapu in southern Tonga through at least Dec. 21. Sustained heavy rainfall could trigger flooding in low-lying communities near streams, creeks, and rivers, as well as in 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 cannot be discounted in steeply sloped terrains. Flooding could isolate some communities for several days. Coastal flooding and abnormally high tides are possible along Fiji's northern and western coasts. In addition to the heavy rain, flooding, and storm surge, the system may produce damaging wind gusts. Widespread and prolonged power outages due to uprooted trees and toppled utility lines are possible. Widespread flooding and storm surge has already been reported, especially in the Yasawa Islands. At least two deaths have been attributed to impacts from the storm.

Transport
Inclement weather associated with the storm could trigger localized business, transport, and utility disruptions through at least Dec. 21. Several road closures have been reported throughout Fij. Floodwaters and debris flows may 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, including Nadi (NAN) and Nausori (SUV) international airports on Viti Levu, Fiji. 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. 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

Joint Typhoon Warning Center
Fiji Meteorological Service
Tonga Meteorological Services