Up to four million people lost power, and transportation ground to a halt; over 5,000 individuals became stranded on ships forced to stay in port during the tropical storm.

Nepartak originated in a region of strong thunderstorm activity, associated with a broad trough of low surface pressure, which was situated around 640 km (400 mi) southeast of Guam by 0000 UTC on November 11.

[1][3] With weak wind shear and modest divergence of air over the system, it began to mature, although initially the Joint Typhoon Warning Center (JTWC)[nb 2] downplayed the potential for tropical cyclogenesis.

[1] At 1800 UTC, the Japan Meteorological Agency (JMA)[nb 3] classified the storm as a tropical depression while it was located northeast of Yap in the Caroline Islands.

Simultaneously, the cyclone entered the area of responsibility of the Philippine Atmospheric, Geophysical and Astronomical Services Administration, which named it Tropical Storm Weng.

[1] At around 1600 UTC on November 13, Nepartak made landfall on northern Samar Island in the Philippines before traversing the remainder of the archipelago from east to west.

[5] The cyclone emerged into the South China Sea briefly weakened and with reduced forward motion, but quickly resumed its intensification trend as it turned more toward the northwest.

With an improving appearance on satellite imagery, however, the storm gained some additional strength, and the JTWC estimated 25W to have attained its first peak intensity with maximum 1‑minute sustained winds of 140 km/h (87 mph) at 0000 UTC on November 16.

A shortwave trough soon cut a weakness in the mid-level ridge which had previously suppressed Nepartak to the south, allowing the cyclone to curve north and enhancing outflow over the storm.

By late on November 17, a small eye feature about 19 km (12 mi) in diameter had formed, and at 0000 UTC the next day it was situated just offshore southwestern Hainan.

[8] Nepartak's winds caused complete power outages on Samar, Masbate, and nearby Marinduque, affecting their entire collective population of nearly four million individuals.

[1][3] Following the storm, a young male sperm whale weighing over 500 kg (1,100 lb) washed ashore near Dongfang City on the island's southern shore, and died shortly after.

Across the Gulf of Tonkin, Vietnam had experienced deadly flooding in the week before Nepartak's approach, and the typhoon initially raised concerns about worsening the situation.