From Sunday to Thursday, however, most of Thailand will experience heavy to very heavy rains as the strong monsoon trough will lie across the North and the Northeast regions into an active low-pressure cell over the middle South China Sea, the department warned.
Meanwhile, the southwest monsoon prevailing over the Andaman Sea, Thailand and the Gulf will strengthen and bring heavy rains and isolated very heavy rains to those areas.
People should beware of flash floods and overflows, especially along waterways and lowland. All transport should take more caution during the thundershowers, the department added.
Areas to be affected by heavy to very heavy rains are:
Sunday
Northeast: Bueng Kan, Sakon Nakhon, Nakhon Phanom, Mukdahan, Yasothon, Amnat Charoen, Si Sa Ket and Ubon Ratchathani.
Central: Kanchanaburi, Ratchaburi, Nakhon Pathom, Samut Songkhram, Samut Sakhon and Bangkok metropolitan.
East: Nakhon Nayok, Prachinburi, Sa Kaeo, Chachoengsao, Chanthaburi and Trat.
South: Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, Ranong, Phang Nga and Phuket.
Monday to Tuesday
North: Chiang Mai, Lamphun, Lampang, Nan, Phrae, Uttaradit, Sukhothai, Phaeng Phet, Phichit, Phitsanulok, Phetchabun and Tak.
Northeast: Udon Thani, Sakon Nakhon, Nakhon Phanom, Mukdahan, Yasothon, Kalasin, Khon Kaen, Chaiyaphum, Nakhon Ratchasima, Maha Sarakham, Roi Et, Amnat Charoen, Buri Ram, Surin, Si Sa Ket and Ubon Ratchathani.
Central: Samut Songkhram, Samut Sakhon, Kanchanaburi, Suphan Buri, Uthai Thani, Chainat, Nakhon Sawan, Lop Buri, Saraburi, Sing Buri, Ang Thong, Ayutthaya, Nakhon Pathom, Ratchaburi and Bangkok metropolitan.
East: Chachoengsao, Nakhon Nayok, Prachinburi, Sa Kaeo, Chonburi, Rayong, Chanthaburi and Trat.
South: Phetchaburi, Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, Songkhla, Ranong, Phang Nga, Phuket, Krabi, Trang and Satun.
Wednesday to Thursday
North: Chiang Mai, Lamphun, Lampang, Nan, Phrae, Uttaradit, Sukhothai, Kamphaeng Phet, Phichit, Phitsanulok, Phetchabun and Tak.
Northeast: Udon Thani, Sakon Nakhon, Nakhon Phanom, Mukdahan, Yasothon, Kalasin, Khon Kaen, Roi Et, Amnat Charoen and Ubon Ratchathani.
Central: Kanchanaburi, Suphan Buri, Uthai Thani, Chainat, Nakhon Sawan, Lop Buri, Saraburi, Sing Buri, Ang Thong and Ayutthaya.
East: Chachoengsao, Nakhon Nayok, Prachinburi, Sa Kaeo, Chonburi, Rayong, Chanthaburi and Trat.
South: Phetchaburi, Prachuap Khiri Khan, Chumphon, Ranong, Phang Nga and Phuket.
The department also forecast waves about 2-3 metres high in the upper Andaman Sea and above 3 metres high during thundershowers in the upper Gulf from July 14-18. All ships should proceed with caution and keep off thundershowers, while small boats should stay ashore throughout the period, it advised.