Temperatures in the North and Northeast of Thailand are expected to drop by 4-7 degrees Celsius by the end of the weekend.
High pressure from China, covering the upper part of the kingdom, will lead to cool or cold weather from Dec 23-26, especially in the North and Upper Northeast, according to the Meteorological Department.
The department said the temperature will be below 16 deg Celsius in many areas, with winds expected, while high mountains will see cold as well as frost in many areas.
From Dec 21-25, strong easterly winds will prevail over the Gulf of Thailand and the South. There will be more rain and isolated heavy rain along the eastern coast of the South.
Waves are likely to be 2-3 metres high.
All ships should proceed with caution and small boats keep ashore, the department said.