With a strong high pressure system prevailing, the temperature in upper Thailand is expected to drop by 1-2 degree Celcius on Jan 14-15, the Thai Meteorological Department said in its 5am forecast on Sunday.
Mountaintops in the North and Northeast will see cold to very cold spells with minimum temperature at 3-9C.
In the South, heavy rain and high waves are predicted on Sunday and Monday in Phatthalung, Songkhla, Pattani, Yala, Narathiwat, Krabi, Trang and Satun provinces due to the strong northeast monsoon prevailing across the Gulf of Thailand and the lower South.
Waves will be 2-3 metres high in the Gulf of Thailand and the Andaman Sea. Residents along the Gulf's coastline are advised to watch for possible inshore surges.
All vessels should proceed with caution and small boats stay ashore until after Jan 15, the department warned.