These conditions are brought about by the monsoon trough lying across the North and the lower Northeast, and the southwest monsoon prevailing across the Andaman Sea, Thailand and the Gulf of Thailand.
The department advised people in affected areas to beware of rain accumulation that may cause flash floods and overflows, especially along foothills near waterways and in low-lying land. Road users should also take more caution during thundershowers, it added.
Meanwhile, waves in the Andaman Sea and the Gulf of Thailand are 1-2 metres high and more than 2 metres in thundershowers. All ships should proceed with caution and keep away from storms, it advised.
The department also said that the Typhoon “Koinu” has downgraded to a severe tropical storm and is expected to move past Hainan Island into the Gulf of Tonkin on Tuesday or Wednesday. This storm has no direct effect on Thailand’s weather.
Provinces likely to be affected by thundershowers on Monday are as follows:
North: Mae Hong Son, Chiang Mai, Lamphun, Lampang, Phrae, Nan, Tak, Sukhothai, Kamphaeng Phet, Uttaradit, Phitsanulok, Phichit and Phetchabun.
Northeast: Loei, Nong Bua Lamphu, Nong Khai, Udon Thani, Chaiyaphum, Khon Kaen, Kalasin, Mukdahan, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima, Buriram, Surin, Sisaket and Ubon Ratchathani.
Central: Nakhon Sawan, Uthai Thani, Lopburi, Saraburi, Ayutthaya, Nakhon Pathom, Samut Sakhon and the Bangkok metropolitan area.
East: Chachoengsao, Nakhon Nayok, Prachinburi, Rayong, Chanthaburi and Trat.
South: Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Pattani, Yala, Narathiwat, Ranong, Phang Nga and Phuket.