Heavy rain raises flash-flood risk in North and Northeast

Heavy to very heavy rain is forecast across upper Thailand through Friday (August 21), with the North and Northeast facing the greatest risk of flash floods and rapid run-off, the Thai Meteorological Department (TMD) warned on Wednesday.

The department issued its ninth warning at 5pm on August 19, advising residents to remain alert to accumulated rainfall, particularly in foothill communities near waterways and in low-lying areas.

The unsettled weather is being driven by a monsoon trough crossing the North and upper Northeast, combined with a relatively strong southwest monsoon covering the Andaman Sea, Thailand and the Gulf of Thailand.

The same conditions are strengthening waves in the upper Andaman Sea and upper Gulf, creating hazardous conditions for small boats and other vessels.

Accumulated rain raises flood danger

The TMD warned that heavy rain combined with earlier rainfall could trigger flash floods and rapid run-off, especially near hillsides, natural drainage channels and low-lying communities.

Motorists should avoid roads with a history of repeated flooding, particularly routes through low-lying areas where temporary inundation could develop quickly.

Residents were advised to plan journeys carefully and monitor further official forecasts and warnings throughout the three-day period.

North faces very heavy rain in seven provinces

Thunderstorms are forecast over 80% of the North from 6pm on Wednesday to 6pm on Thursday, with heavy rain expected across many areas.

Heavy rain is forecast in Chiang Mai, Chiang Rai, Phayao, Lamphun, Sukhothai, Tak, Kamphaeng Phet and Phichit.

Very heavy rain is possible in Mae Hong Son, Lampang, Nan, Phrae, Uttaradit, Phitsanulok and Phetchabun.

Temperatures will range from lows of 22–27C to highs of 28–34C, with southwesterly winds of 10–20 kilometres per hour.

Northeast also sees 80% storm coverage

Thunderstorms are also expected over 80% of the Northeast, with heavy rain across Nong Bua Lamphu, Chaiyaphum, Khon Kaen, Maha Sarakham, Roi Et, Yasothon, Amnat Charoen, Nakhon Ratchasima, Buriram, Surin, Si Sa Ket and Ubon Ratchathani.

Very heavy rain is forecast in parts of Loei, Nong Khai, Bueng Kan, Udon Thani, Sakon Nakhon, Nakhon Phanom, Kalasin and Mukdahan.

Minimum temperatures will range from 22–25C and maximum temperatures from 27–32C. Southwesterly winds will reach 10–20 kilometres per hour.

Heavy rain extends to Central region and East

The Central region will have thunderstorms over 60% of its area, with heavy rain possible in Nakhon Sawan, Phra Nakhon Si Ayutthaya, Lop Buri, Saraburi, Kanchanaburi and Ratchaburi.

Temperatures will range from 23–26C at night to 32–36C during the day, with southwesterly winds of 10–25 kilometres per hour.

The East will see thunderstorms over 70% of the region. Heavy rain is forecast in Nakhon Nayok, Prachin Buri, Sa Kaeo, Chachoengsao and Chanthaburi, while Trat could receive very heavy rain.

Temperatures in the East will range from 23–28C to 31–34C, with southwesterly winds of 20–40 kilometres per hour.

Waves off the eastern coast will reach 2–3 metres and exceed 3 metres during thunderstorms.

Bangkok has 60% storm coverage

Bangkok and surrounding provinces will have thunderstorms over 60% of the area, with isolated heavy rain.

Minimum temperatures will range from 25–27C and maximum temperatures from 33–35C. Southwesterly winds will reach 10–25 kilometres per hour.

Small boats told to remain ashore

Waves in the upper Andaman Sea and upper Gulf will reach 2–3 metres and rise above 3 metres in thunderstorms.

The lower Andaman Sea will have waves of about 2 metres, increasing to more than 2 metres in stormy areas.

All vessels in the Andaman Sea and Gulf of Thailand should proceed cautiously and avoid thunderstorms. Small boats in the upper Andaman Sea and upper Gulf should remain ashore through August 21.

Southern coasts face scattered thunderstorms

The eastern coast of the South will have thunderstorms over 40% of the region, mainly in Phetchaburi, Prachuap Khiri Khan, Chumphon and Surat Thani. Temperatures will range from 23–27C to 33–36C.

From Surat Thani northwards, southwesterly winds will reach 20–35 kilometres per hour. Waves will be 1–2 metres high, rising above 2 metres offshore and during thunderstorms.

From Nakhon Si Thammarat southwards, winds will reach 15–35 kilometres per hour. Waves will be about 1 metre near the coast and 1–2 metres offshore, exceeding 2 metres in thunderstorms.

The western coast of the South will also have thunderstorms over 40% of the area, with isolated heavy rain in Ranong. Temperatures will range from 23–27C to 31–34C.

From Phuket northwards, winds will reach 20–40 kilometres per hour and waves will be 2–3 metres, rising above 3 metres during thunderstorms.

From Krabi southwards, winds will reach 20–35 kilometres per hour. Waves will be about 2 metres and exceed 2 metres in thunderstorms.

The public can follow updates through the TMD website or contact the department around the clock on 1182 or 0-2399-4012-13.