Heavy rain and thunderstorms were forecast from Nghe An Province to northern Quang Tri Province in Vietnam on September 25.
Some areas had already received heavy rain that day, and the risk around mountainous areas and waterways increased as the soil absorbed more water.
What matters in this alert is not only the daily accumulation, but also the possibility of rain concentrated within a short period and strong winds at sea.
3-Line Summary
1. Heavy rain was forecast from Nghe An to northern Quang Tri
2. Heavy rain exceeding 80mm in 3 hours was warned
3. The risk is increasing around mountainous areas and small streams
From Nghe An to Northern Quang Tri, Locally Exceeding 120mm
The National Center for Hydro-Meteorological Forecasting of Vietnam forecast 20~50mm of rain from Nghe An Province to northern Quang Tri Province on September 25, with some areas potentially exceeding 120mm. It particularly warned of the possibility of heavy rain exceeding 80mm in 3 hours.
This means that, just as when rain continues for a long time, drainage systems and the ground may struggle when rain is concentrated within a short period. A local Quang Tri media outlet reported that 41mm was recorded at the Tan Tan1 observation station in Thanh Hoa Province and 46.2mm at the Phu Gia observation station in Ha Tinh Province between the night of the 24th and the early morning of the 25th. These figures are observed rainfall amounts at that time, not forecasts.
The forecast continues from the night of the 25th through the 26th. Rain of 20~40mm was expected from Nghe An Province to northern Quang Tri Province, with some areas expected to receive more than 80mm. However, this was a forecast by the meteorological authorities, so the actual location and amount of rainfall were not confirmed results.
Already-Wet Ground Increases the Risk of Landslides and Flash Floods
The Voice of Vietnam reported that alerts for flash floods, landslides, and ground subsidence had been issued on the morning of the 25th for Thanh Hoa Province, Ha Tinh Province, Quang Tri Province, Da Nang City, and Quang Ngai Province. According to the report, soil moisture in some areas exceeded 85% or was close to saturation.
The observed rainfall amounts were also considerable. The basin of the Trung Thuan Reservoir in Quang Tri Province recorded 128mm, the Phuoc Thanh area of Da Nang City recorded 126mm, and the Son Tay area of Quang Ngai Province recorded 107mm. The meteorological authorities explained that if the rain continues, the risks of flash floods in small streams, landslides on slopes, and flooding in low-lying areas, cities, and industrial complexes may increase.
The key point of this alert is not simply that there has been a lot of rain. Because strong rain is falling again on soil that has already absorbed water, areas near mountains and small streams require consideration of both the terrain and ground conditions, rather than cumulative rainfall alone.
Squalls and High Waves at Sea as Well as on Land
At sea, showers and thunderstorms were expected in the southern Gulf of Tonkin, waters from south of Quang Tri Province to Ca Mau Province, the Gulf of Thailand, and the central and southern South China Sea. It warned that whirlwinds, 7~8-grade squalls, and waves exceeding 2m could occur during thunderstorms.
The People’s Daily of Vietnam also reported that rain and thunderstorms would continue in the Central Highlands and the south, and that caution was needed regarding flash floods in small streams and landslides on slopes in mountainous areas. In areas receiving heavy rain, the possibility of squalls, lightning, and hail was also noted.
References
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