
The Bangkok metropolitan area could experience thundershowers in 60 percent of the area, mostly during the afternoon and late evening, it added.
The rains are the result of a weakening southwest monsoon prevailing over the Andaman Sea and the Gulf, and the weak monsoon trough that lies across Myanmar and upper Laos combined with the low-pressure cell over upper Vietnam and Tonkin Bay.
People should beware of flash floods and overflows, especially along waterways and lowlands, the department warned, adding that all forms of transport should exercise caution during thundershowers.
The department also advised all ships to proceed with caution, especially in the Andaman Sea and the upper Gulf, where wave height could rise to more than 2 metres during storms.
With tropical storm Lan now covering the North of Japan, the department advised those who plan to travel there to follow the latest weather updates and organise their trip accordingly.