The Meteorological Department forecast is for heavy rain in the lower South, high waves along the eastern coast of the South, and cold weather and thunderstorms in the upper North.
Wanchai Sakudomchai, director-general of the department, said the strong northeastern monsoon over the South and the Gulf of Thailand and a low pressure area above the Strait of Malacca and Malaysia were bringing heavy rain in the lower South.
This would mainly affect Chumphon, Krabi, Narathiwat, Nakhon Si Thammarat, Pattani, Phatthalung, Satun, Songkhla, Surat Thani, Trang and Yala provinces. People in the southern provinces were warned of possible flash floods and runoff.
Small boats were advised to stay ashore along the eastern coast of the South due to powerful waves.
In Narathiwat province, local administrators and soldiers were handing out food to about 1,000 people in Moo 2 and Moo 3 villages of tambon Bang Tong in Rueso district that have been isolated by two-metre-deep floodwater for a week.
Flooding was also reported from Chumphon, Krabi, Nakhon Si Thammarat, Pattani, Phatthalung, Satun, Songkhla, Surat Thani, Trang, and Yala.
Winds from Myanmar are bringing thunderstorms to the upper North - Chiang Mai, Chiang Rai, Lampang, Lamphun, Mae Hong Son, Nan, Phayao and Phrae provinces. A high pressure system is also causing cold weather in the upper part of the country.
From Thursday to next Monday temperatures in the upper part of the country are expected to rise 1-3°C as the high pressure area weakens, the weather office said.