# Tropical Storm Sonca (2017)

Tropical Storm Sonca was a weak tropical cyclone that impacted Indochina during the end of July 2017. As the 10th named storm of the 2017 Pacific typhoon season, Tropical Storm Sonca formed south of Hong Kong, after drifting westward for multiple days, the storm intensified into a tropical storm, receiving the name Sonca. The storm later affected Hainan, reaching its peak intensity. On July 25, the storm made landfall over the Quảng Trị province, then dissipated.
The storm killed 37 people, with a damage of $313 million USD. In Vietnam, 1,500 houses were damaged, with an impact of $13 million USD. The storm also affected Cambodia, killing three people and destroying 2686 houses. Thailand was the most affected, with 23 fatalities.

## Meteorological history

On July 21, both the JMA and the JTWC reported that Tropical Depression 08W had developed approximately 582 km (361 mi) to the south of Hong Kong. The storm had a rapidly consolidating low-level circulation center. The storm had a favorable environment, with slight improvement of poleward outflow. The JTWC later assessed the certainty to intensity to a tropical cyclone as poor, assessing multiple problems, such as poor initialization and small size. The next day, the storm had a favorable environment still, with vertical windshear offset by poleward outflow. The JTWC still kept their certainty as poor. On the early hours of the next day, the JTWC upgraded their certainty to good based on newly uncovered satellite footage, the JTWC also designated the system as a tropical storm. After drifting westward for a couple of days, the system strengthened into a tropical storm by JMA while nearing the island province of Hainan, receiving the name Sonca.
13 hours later, the storm was pulled southward by a building direction. Just before the storm had its peak intensity, the storm rapidly intensified after reports of a consolidating low-level circulation center. The storm later accelerated north after a steering ridge reoriented the storm. By July 24, Sonca reached its maximum intensity with a minimum pressure of 994 hPa. Early on July 25, the JTWC issued its final advisory as the system made landfall over in the Quảng Trị Province, Vietnam.

## Preparations and impact
### Vietnam

During the storm, heavy floods were recorded in Vietnam, causing catastrophic property damage, submerging 229 villages. A Telegram was sent to send firefighters and police to rescue people in the northern provinces of Vietnam.
At least six people were killed when the storm made landfall on July 25, all in the provinces of Hà Tĩnh and Quảng Trị. Also, about 1,500 houses were damaged in these two provinces. Across the whole of Vietnam, roughly 5,777 hectares (14,280 acres) of paddy fields and 750 hectares (1,900 acres) of croplands were damaged. In Nghe An Province, the total damage caused by the storm reached 127 billion dong (US$5.6 million). Total damage in Vietnam reached 300.7 billion dong (US$13 million).

### Cambodia

Tropical Storm Sonca affected four provinces across Cambodia, at least three people died, and 2686 houses were submerged. 53 households were also affected. In the Choam Khsant District, 48 families had to be evacuated because of the storm. Heavy floods affected four provinces, with 550 affected families and at least 1000 displaced residents. The National Committee for Disaster Management for Cambodia warned fishermen about the rough weather from the storm.

### Thailand

Flash floods across Thailand killed 23 people and affected 44 out of 76 provinces in Thailand. The hardest hit province was Sakon Nakhon, Northeast Thailand as the storm forced the closer of Sakon Nakhon Airport lasting for 3 days. Damages in Sakon Nakhon exceeded 100 million baht (US$3 million). The floods created by the storm were the strongest floods in Thailand for two decades.
Heavy rain damaged bridges in Khon Kaen province and flooded buildings in Ubon Ratchathani province and Sisaket province, where some people were relocated to temporary accommodations. In Lopburi province, some people were rescued by boat after the roads became impassable. In Sukhothai province, the Yom River flooded, and sandbags were used to help contain the floodwaters. Trains had to be re-routed in Nong Khai province when telephone poles fell on the tracks.
In total, the damage from flooding triggered by the storm in Thailand reached 10 billion baht (US$300 million).