TMD forecasts heavier rain across Thailand and Bangkok

Thailand is forecast to become wetter from September 8–10, with isolated very heavy rain expected in Bangkok and surrounding provinces, the lower North, lower Northeast, Central region, East and the South’s west coast, according to the Thai Meteorological Department (TMD).

The department’s September 4–10 forecast places the North and Northeast at particular risk of heavy to very heavy downpours during the first part of the period. Rain will then increase more widely as the monsoon trough shifts south.

Bangkok and surrounding provinces are forecast to have thunderstorms across 70–80% of the area from September 8–10, with isolated heavy rain and very heavy falls in some places on September 10.

Separately, the Department of Mineral Resources has asked its volunteer networks in 16 provinces to monitor landslide and flash-flood risks from September 4–6.

Monsoon shift brings more widespread rain

From September 4–7, a monsoon trough lies across the North and upper Northeast, while a moderate southwest monsoon covers the Andaman Sea, Thailand and the Gulf of Thailand. These conditions are bringing isolated heavy to very heavy rain to upper Thailand, particularly the North and Northeast. 

During September 8–10, the trough is expected to move across the lower North, upper Central region and Northeast towards a low-pressure area over the central South China Sea. The southwest monsoon will remain moderate, bringing heavy rain to many areas and isolated very heavy downpours in the regions identified by the department.

Winds and waves in the Andaman Sea and Gulf of Thailand will remain moderate throughout the forecast period. Waves in the upper Andaman Sea will reach about 2 metres, compared with 1–2 metres in the lower Andaman Sea and upper Gulf. Waves will exceed 2 metres in thunderstorms. 

The department advises the following precautions throughout the period.

• Watch for flash floods and rapid run-off caused by heavy to very heavy rain and accumulated rainfall, particularly on foothill slopes near waterways and in low-lying areas.
• Avoid routes prone to repeated flooding, especially low-lying roads where water may accumulate temporarily.
• Navigate boats cautiously and avoid areas affected by thunderstorms.

Regional forecast for September 4–10

The percentages below indicate the proportion of each region forecast to experience thunderstorms.

North

• Thunderstorms across 60–80% of the region throughout the period, with isolated heavy rain. Some areas face very heavy rain on September 4–5 and September 9–10.
• Variable winds at 10–20 kilometres per hour.
• Minimum temperatures of 23–28°C and maximum temperatures of 28–36°C.

Northeast

• Thunderstorms across 60–80% of the region throughout the period, with isolated heavy rain. Some areas face very heavy rain on September 4–6 and September 8–10.
• September 4–7 — Southwesterly winds at 10–20 kilometres per hour.
• September 8–10 — Variable winds at 10–20 kilometres per hour.
• Minimum temperatures of 23–27°C and maximum temperatures of 28–35°C.

Central region

• September 4–7 — Thunderstorms across 60–70% of the region, with isolated heavy rain.
• September 8–10 — Thunderstorms across 70–80% of the region, with isolated heavy rain and very heavy falls in some areas on September 9–10.
• Southwesterly winds at 10–20 kilometres per hour.
• Minimum temperatures of 23–27°C and maximum temperatures of 30–36°C.

East

• September 4–7 — Thunderstorms across 60–70% of the region, with isolated heavy rain.
• September 8–10 — Thunderstorms across 70–80% of the region, with isolated heavy to very heavy rain.
• Throughout the period, southwesterly winds at 15–35 kilometres per hour. Waves of 1–2 metres, exceeding 2 metres in thunderstorms.
• Minimum temperatures of 23–28°C and maximum temperatures of 29–34°C.

South, east coast

• September 4–7 — Thunderstorms across 30–40% of the region.
• September 8–10 — Thunderstorms across 40–60% of the region, with isolated heavy rain.
• Throughout the period, southwesterly winds at 15–35 kilometres per hour. Waves of about 1 metre near the coast and 1–2 metres offshore, exceeding 2 metres in thunderstorms.
• Minimum temperatures of 23–27°C and maximum temperatures of 31–36°C.

South, west coast

• September 4–7 — Thunderstorms across 40–60% of the region, with isolated heavy rain.
• September 8–10 — Thunderstorms across 60–80% of the region, with isolated heavy to very heavy rain.
• From Phuket northwards throughout the period, southwesterly winds at 20–35 kilometres per hour and waves of about 2 metres, exceeding 2 metres in thunderstorms.
• From Krabi southwards throughout the period, southwesterly winds at 15–35 kilometres per hour and waves of 1–2 metres, exceeding 2 metres in thunderstorms.
• Minimum temperatures of 23–27°C and maximum temperatures of 28–34°C.

Bangkok and surrounding provinces

• September 4–7 — Thunderstorms across 60–70% of the area, with isolated heavy rain on September 5–6.
• September 8–10 — Thunderstorms across 70–80% of the area, with isolated heavy rain and very heavy falls in some places on September 10.
• Southwesterly winds at 10–20 kilometres per hour.
• Minimum temperatures of 25–28°C and maximum temperatures of 31–35°C.

Landslide and flash-flood watch in 16 provinces

The Department of Mineral Resources, under the Ministry of Natural Resources and Environment, has asked its volunteer networks to monitor the following districts for landslides and flash floods from September 4–6.

North

• Mae Hong Son — Mueang Mae Hong Son, Sop Moei, Mae Sariang, Mae La Noi, Khun Yuam, Pang Mapha and Pai.
• Tak — Tha Song Yang, Mae Ramat, Umphang, Mae Sot and Phop Phra.
• Chiang Mai — Omkoi, Hot, Samoeng, Mae Taeng, Mae Chaem, Mae Ai, Chiang Dao, Fang and Chom Thong.
• Chiang Rai — Mueang Chiang Rai, Mae Fa Luang, Mae Suai, Wiang Pa Pao, Thoeng, Mae Lao, Chiang Saen and Mae Sai.
• Nan — Mueang Nan, Pua, Bo Kluea, Tha Wang Pha, Mae Charim, Santi Suk, Song Khwae, Thung Chang, Chiang Klang, Wiang Sa, Na Noi, Na Muen, Ban Luang and Chaloem Phra Kiat.
• Phrae — Mueang Phrae, Song, Wang Chin and Rong Kwang.
• Lampang — Ngao, Wang Nuea and Chae Hom.
• Uttaradit — Tha Pla, Laplae, Nam Pat, Fak Tha and Ban Khok.
• Phetchabun — Mueang Phetchabun, Chon Daen, Lom Kao, Lom Sak and Khao Kho.
• Phitsanulok — Mueang Phitsanulok, Chat Trakan, Nakhon Thai, Noen Maprang and Wang Thong.

Central region

• Kanchanaburi — Sangkhla Buri, Thong Pha Phum, Sai Yok, Dan Makham Tia and Si Sawat.

East

• Trat — Ko Chang, Bo Rai and Khao Saming.

Northeast

• Loei — Dan Sai, Chiang Khan, Na Haeo, Phu Ruea, Pak Chom and Wang Saphung.
• Ubon Ratchathani — Buntharik, Nam Yuen and Na Chaluai.
• Udon Thani — Na Yung and Nam Som.
• Nong Khai — Sangkhom.