The increased rainfall, which could cause flash flooding and forest runoff especially in hilly areas near waterways and low-lying areas, is due to a monsoon trough passing through the northern and upper northeastern regions and combining with a low-pressure system along the central coast of Vietnam.
Wave height in the Andaman Sea and the Gulf of Thailand will be moderate, rising to 1-2 metres in the upper Andaman and Gulf, higher in thunderstorms.