Thailand is forecast to experience increased rainfall from Sunday through Friday, the Meteorological Department said on Saturday morning.
The East and western areas in the South will be the most heavily affected, forecasters said.
A monsoon trough lying across the North and upper Northeast has coincided with southwesterly winds covering the Andaman Sea, Thailand and the Gulf of Thailand.
Flash floods and forest runoff are possible, especially in areas near foothills and streams, the department warned.
Provinces forecast to face very heavy rain during the period are:
Sunday: Trat, Ranong and Phangnga
Monday: Tak, Kanchanaburi and Trat
Tuesday: Chanthaburi, Trat, Ranong and Phangnga
Wednesday: Chanthaburi, Trat, Chumphon, Ranong and Phangnga
Thursday: Bueng Kan, Chanthaburi, Trat, Chumphon, Ranong and Phangnga
Friday: Kanchanaburi, Chanthaburi and Trat.
Widespread rain is also expected on Saturday, particularly in the western South, the East and the Central Plains, including Bangkok.