These areas could see flash flooding and forest run-off, especially near water courses and in low-lying areas.
These weather conditions are caused by a monsoon trough passing over the upper part of southern Thailand, the Gulf of Thailand and the eastern region combining with the southwest monsoon.
A high-pressure system and a cool air mass, meanwhile, will prevail over the northern, central, and northeastern regions.
As for the sea conditions, the Andaman Sea and the Gulf of Thailand will see waves of approximately 1 metre, more in thunderstorms. Small vessels are advised to navigate with caution.