The colder weather is a result of a rather strong high-pressure system covering Thailand and the South China Sea, the department said, adding that the westerly trough from Myanmar will also move through the North and the upper Central regions on Thursday, bringing strong winds and isolated rains to the upper part of the country.
The department advised people in this region to take care of their health due to changing weather, and to be aware of fire risks due to strong winds and dry air.
Meanwhile, the northeast monsoon prevailing over the Gulf and the South will strengthen on Thursday, bringing isolated heavy rain to the lower South that will last until Saturday.
Residents of the lower South should watch out for flash floods and overflows, especially near foothills, waterways and lowland areas. Residents along the Gulf shore should also beware of inshore surges.
For sea conditions, waves in the lower Gulf could rise up to 2-3 metres high and above 3 metres in thundershowers, while those in the upper Gulf and the Andaman Sea are about 2 metres high.
All ships should proceed with caution and keep out of thundershowers, the department said, adding that small boats in the lower Gulf should stay ashore until Saturday.