The sixteenth named storm of the annual typhoon season, the precursor of Sanba formed as a low-pressure area on October 13, west of the Philippines.

The precursor of Sanba interacted with the Intertropical Convergence Zone (ITCZ), which brought heavy rains to Vietnam, sinking two fishing boats, killing three people and 12 other were missing.

Due to its slow-paced movement, Sanba brought strong winds and heavy rains in Hainan and Liangguang region.

On October 13, a low-pressure area formed in the South China Sea, west of the Philippines, in which the system interact with the Intertropical Convergence Zone (ITCZ).

[1][2] The Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert (TCFA) at 22:00 UTC for the low-pressure area, while the system located just off the coast of Central Vietnam, analyzing the system in a favorable environment such as high sea surface temperature of 28–29 °C (82–84 °F), extremely strong divergence, and moderate wind shear.

[5] Infrared satellite imagery depicts a central dense overcast (CDO) obscuring the circulation of a poorly organized depression.

[11] Later that day, Sanba attained its peak intensity with 10-minute sustained winds of 45 mph (75 km/h) and a barometric pressure of 1,000 hPa (29.53 inHg).

[13] The system began to turn southward and gradually weakened because of unfavorable conditions such as land interaction, cold together with dry air, and strong wind shear.

[18] The precursor of Sanba interacted with the ITCZ and brought thunderstorms, tornadoes and strong waves in the South China Sea, sinking two Vietnamese fishing boats near the Spratly Islands.

[24][25] The interaction between Sanba and the ITCZ, along with cold air and easterly winds blowing in from the sea, caused heavy rain in Central Vietnam, with many places recording rainfall of 120–175 mm (4.7–6.9 in) in 8 hours.

[32][33] The impact of Sanba in northern Vietnam is relatively minor, only Bạch Long Vĩ Island recorded near gale-force winds.

[46] In addition, due to the effects of Sanba offshore, a Chinese cargo ship were trapped in the Gulf of Tonkin, west of Weizhou Island.

[44] Due to the combined effects of Sanba (including its precursor) and the northeast monsoon, Hong Kong and Macau experienced some rainfall and gusty winds.