Temperatures are expected to drop sharply in upper Thailand over the next week due to a high pressure system moving in from China, according to the Meteorological Department.
Director-general Somsak Khaosuwan said on Tuesday that temperatures in the North and the Northeast would fall by 8-10°C through to next Tuesday.
On mountaintops temperatures would drop to 1-9°C and there could be frost. In lower areas, temperatures were expected at 10-15°C, he said.
In the Central Plains and the East, a 6-8°C drop is forecast, to 15-20°C, during the same period, Mr Somsak said.
Waves in the Gulf of Thailand southwards from Chumphon province would be 2-4 metres high.
Small boats are warned to stay ashore.