An early cyclone blew across the South China Sea, bringing heavy rain and flooding to the Philippines in early January, 2013. Tropical Storm Sonamu (01W) was the earliest storm to form in the Northwest Pacific in the last 34 years, since Typhoon Alice in 1979.
The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASAís Aqua satellite captured this true-color image on January 4 at 0523 UTC (12:35 a.m. EST). By 1500 UTC (10:00 a.m. EST) Sonamuís maximum sustained winds were blowing at 40.2 mph (64.8 km/h) and the stormís center was located near 8.9 N latitude and 113.2 E longitude, about 495 miles (796 km) east-southeast of Ho Chi Minh City, Vietnam. It was moving towards the west at about 16 mph (26 km/h) in the direction of southern Vietnam.
On Sunday, January 6, Tropical Storm Sonamuís maximum sustained winds were near 46 mph (74 km/h) and the center was located about 259 miles (416 km) southeast of Ho Chi Min City, and still moving west. On that day, the low level center became exposed to outer winds, which pushed the strongest convection and heaviest rainfall to the north due to the strong wind shear.
By January 7, wind shear and intrusion of dry air had taken its toll on the storm, and Sonamu weakened to a tropical depression. Its track had curved to the southwest, and slowed. It was expected to track southerly and miss the Malay Peninsula.