The Office of the National Water Resources (ONWR) has warned 20 provinces to prepare for possible flash floods, forest runoff, landslides and river overflows from Aug 2-4 as heavy rain is forecast in several regions.
The warning was issued on Sunday as an intensifying monsoon trough and strengthening southwesterly monsoon are expected to bring heavy to very heavy rain, particularly to the North, Northeast, East and South.
The agency said a monsoon trough stretching across Myanmar and northern Laos into a low-pressure cell, combined with stronger southwesterly winds, would affect several parts of the country.
ONWR urged residents to monitor flood risks, especially in urban areas with poor drainage and locations vulnerable to flash floods, forest runoff, landslides and river overflows.
The provinces under warning are Chiang Rai, Chiang Mai, Lampang, Nan and Phetchabun; Loei, Nong Khai, Udon Thani, Bueng Kan, Sakon Nakhon and Nakhon Phanom; Chanthaburi and Trat; and Ranong, Phangnga, Phuket, Krabi, Pattani, Yala and Narathiwat.
The agency said heavy rain could continue in parts of the upper Northeast, East and Andaman coast until Aug 7 as the monsoon trough remains active and the southwesterly monsoon strengthens.
Separately, the Meteorological Department (TMD) forecast widespread rain across the North and upper Northeast, with heavy rain in some areas, from Aug 2-10. It warned that accumulated rainfall could trigger flash floods and forest runoff.
Moderate winds and waves are forecast in the Andaman Sea and Gulf of Thailand, with waves reaching 1-2 metres in the upper Andaman Sea and about 1 metre elsewhere, rising above 2 metres during thunderstorms. Mariners were advised to exercise caution and avoid stormy areas.
The TMD said the monsoon is expected to strengthen during Aug 7-9 under the influence of Typhoon Dolphin, which is moving east of China.
