The Meteorological Department on Sunday warned residents in 10 provinces of the lower Central Plains and the South to brace for heavy downpours and strong winds over coming days.
Wanchai Sakudomchai, its director-general, said severe rain and strong winds will hit much of Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Ranong, Phangnga, Phuket and Krabi over the next few days.
The active low-pressure cell over the lower South China Sea will move west slowly through the Gulf of Thailand, the South and the Andaman Sea between Monday and Friday.
There will likely be abundant rain over the South, it said.
The department also warned residents of those provinces to beware of possible flash floods. There is a possibility of strong wind waves in the Gulf of Thailand and the Andaman Sea rising 2-3 metres high, its forecasters predict.
All ships should proceed with caution, and small boats should be kept ashore, it said. It also asked people to closely monitor weather updates.
Interior Minister Anupong Paojinda said Sunday he was concerned about the weather situation in the South. He has ordered the Disaster Mitigation and Prevention Department to work closely with southern provinces to brace for floods.
Gen Anupong said machines and officials are on standby to help the affected until the situation returns to normalcy.
Meanwhile, the Ministry of Agriculture and Cooperatives' working group on water management is devising three plans to improve water flow capacity in the eastern side of the Chao Phraya River.
Once the plans are complete, they will be forwarded to the National Water Resources Commission for initial approval.
Then the commission will submit them to the cabinet for consideration next month, said Agriculture and Cooperatives Minister Chatchai Sarikulya.
Gen Chatchai said the three plans initiated to improve water flow capacity were being drafted in line with Prime Minister Prayut Chan-o-cha's order for the ministry to have plans in place to limit flood impacts along the river basin.
He said substantive plans were needed to prevent critical flooding in the future.
Gen Chatchai said the working group agreed in principle that it should have a new canal to link Bang Ban and Bang Sai districts in Ayutthaya to improve water flow capacity as the current canal has bends in its structure, which lowers the speed of water flow.
He said the first plan would be able to limit flooding in Ayutthaya and Ang Thong provinces.
The newly-made 22 kilometre canal could allow water flow at a capacity of 1,200 cubic metres per second.
The second plan is to increase water flow in Chai Nat-Pasak canal from 200 cu/m per second to 930 cu/m per second, he said.
However, Gen Chatchai said the working group still had different ideas about the third plan -- whether it should build a new 130 km canal from Pasak River in Lop Buri province to the Gulf of Thailand in Samut Prakan province, or construct a waterway along the Third Outer Ring Road in Ayutthaya to link with the Gulf of Thailand.