Sonamu has left the Philippines and Palawan behind and NASA satellite imagery showed the storm intensified into a tropical storm while moving through the easternmost South China Sea.
At Jan. 4, 2013 at 0535 UTC (12:35 a.m. EST), a visible image of Tropical Storm Sonamu was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument that flies aboard NASA's Aqua satellite.
The Joint Typhoon Warning Center (JTWC) noted that some animated infrared satellite imagery shows central convection persisting over the low level circulation center and some fragmented formative banding over the northern semi-circle.
By 1500 UTC (10 a.m. EST/U.S.), Sonamu's maximum sustained winds had increased to near 35 knots (40.2 mph/64.8 kph). Sonamu's center was located near 8.9 north latitude and 113.2 east longitude, about 430 nautical miles (494.8 miles/ 796.4 km) east-southeast of Ho Chi Minh City, Vietnam. Sonamu is moving to the west at 14 knots (16.1. mph/26 kph) and is expected to continue in that general direction for the next couple of days with its center staying over open waters as it passes southern Vietnam.
Extreme southern Vietnam, from near Ho Chi Minh City southward may feel the effects of the outer fringes of the storm, with gusty winds, heavy rainfall, and rough coastal conditions.
JTWC forecasters expect that Sonamu will peak in intensity sometime on Jan. 5 and then weaken as vertical wind shear increases.
Sonamu is forecast to turn to the south-southwest and make landfall early next week in east central Malaysia.