Which provinces face heavy rain from strong tropical storm Wipha?

The Thai Meteorological Department has issued its fourth warning on strong tropical storm Wipha, which is expected to bring widespread heavy to very heavy rainfall across several regions of Thailand between July 20–24.

As of 4pm on Sunday, July 20, Wipha was classified as a strong tropical storm located in the upper South China Sea, with its centre over Jiangmen, Guangdong province in China (latitude 21.8°N, longitude 112.8°E). The storm was packing maximum sustained winds near the centre of approximately 110 kilometres per hour and was moving westward at around 25 km/h.

The storm is forecast to cross southern China and enter the Gulf of Tonkin before making landfall in northern Vietnam between July 21–22. It is expected to weaken gradually into a tropical depression and then into a low-pressure system, moving along the monsoon trough extending over upper Laos and northern Thailand.

At the same time, a strong southwest monsoon is prevailing over the Andaman Sea, Thailand, and the Gulf of Thailand. The interaction between this monsoon and strong tropical storm Wipha will intensify rainfall over large parts of the country.

Expected Impact

From July 20–24, northern, upper northeastern, central (western), eastern, and western southern Thailand are expected to experience heavy to very heavy rain, raising the risk of flash floods and runoffs, particularly in low-lying areas and near foothills and waterways.

Authorities are urging residents in at-risk areas to stay alert for potential flooding and landslides.

Provinces forecast to be affected:

July 20:

North: Chiang Rai, Phayao, Nan, Phrae, Uttaradit, Phichit, Phitsanulok, Phetchabun, Kamphaeng Phet, Tak

Northeast: Nong Khai, Bueng Kan, Udon Thani, Sakon Nakhon, Nakhon Phanom, Kalasin, Mukdahan, Yasothon, Amnat Charoen, Ubon Ratchathani

Central: Lop Buri, Saraburi, Kanchanaburi, Ratchaburi, Samut Songkhram, Samut Sakhon, Nakhon Pathom

East: Nakhon Nayok, Prachin Buri, Rayong, Chanthaburi, Trat

South (west coast): Phetchaburi, Prachuap Khiri Khan, Surat Thani, Chumphon, Ranong, Phangnga, Phuket, Krabi

July 21:

North: Mae Hong Son, Chiang Mai, Chiang Rai, Phayao, Nan, Phrae, Uttaradit, Kamphaeng Phet, Phichit, Phitsanulok, Phetchabun, Tak

Northeast: Loei, Nong Khai, Bueng Kan, Nong Bua Lamphu, Udon Thani, Sakon Nakhon, Nakhon Phanom, Mukdahan

Central (including Bangkok): Nakhon Sawan, Uthai Thani, Chai Nat, Lop Buri, Saraburi, Sing Buri, Ang Thong, Ayutthaya, Suphan Buri, Kanchanaburi, Ratchaburi, Nakhon Pathom, Samut Songkhram, Samut Sakhon

East: Nakhon Nayok, Prachin Buri, Rayong, Chanthaburi, Trat

South (west coast): Phetchaburi, Prachuap Khiri Khan, Chumphon, Ranong, Phang Nga

July 22–24:

North: Mae Hong Son, Chiang Mai, Chiang Rai, Lamphun, Lampang, Phayao, Nan, Phrae, Uttaradit, Sukhothai, Phitsanulok, Phichit, Phetchabun, Kamphaeng Phet, Tak

Northeast: Loei, Nong Bua Lamphu, Udon Thani, Nong Khai, Bueng Kan, Sakon Nakhon, Nakhon Phanom, Chaiyaphum, Khon Kaen, Kalasin, Mukdahan, Yasothon, Amnat Charoen, Nakhon Ratchasima, Ubon Ratchathani

Central: Nakhon Sawan, Uthai Thani, Chai Nat, Sing Buri, Ang Thong, Suphan Buri, Lop Buri, Saraburi, Kanchanaburi, Ratchaburi, Ayutthaya

East: Nakhon Nayok, Prachin Buri, Rayong, Chanthaburi, Trat

South (west coast): Phetchaburi, Prachuap Khiri Khan, Ranong, Phangnga

For upper Andaman Sea , waves are forecast to reach 2–4 metres, and could exceed 4 metres in areas with thunderstorms. In the lower Andaman Sea and upper Gulf of Thailand, waves are expected to rise to 2–3 metres, exceeding 3 metres offshore and in stormy areas.

The TMD advises all vessels to navigate with caution and avoid areas with thunderstorms. Small boats in the Andaman Sea and upper Gulf of Thailand should remain ashore during this period.

Authorities warn of possible flash floods, runoffs, and landslides, especially in low-lying areas, along foothills and near waterways. Residents are advised to stay updated and follow evacuation protocols if the situation escalates. 

The TMD will issue its next advisory at 11pm on July 20.

For updates, visit www.tmd.go.th or call 0-2399-4012-13, or hotline 1182, available 24/7.

Expert analysis: Wipha unlikely to match the strength of Super Typhoon Yagi

Assoc Prof Thon Thamrongnawasawat from Kasetsart University’s Faculty of Fisheries posted a Facebook analysis comparing strong tropical storm Wipha to Super Typhoon Yagi from last year.

He explained that tropical cyclones range from depressions (≤62 km/h) to tropical storms (63–118 km/h), and typhoons (≥119 km/h). As of now, Wipha is classified as a strong tropical storm, with winds reaching around 118 km/h—just shy of typhoon status. Some reports now put wind speeds at 120 km/h, qualifying it as a Category 1 typhoon, though it remains officially a tropical storm.

In contrast, Super Typhoon Yagi in September last year reached speeds of 260 km/h, over twice as powerful as Wipha. Yagi gained energy over the open sea before slamming into Hainan and northern Vietnam as a Category 3–4 typhoon. Wipha, by comparison, made landfall in Hong Kong as a strong tropical storm and is projected to graze the coastlines of Hainan and northern Vietnam.

Thon noted that Wipha’s proximity to land may prevent it from gaining further strength. Forecast models from the TMD suggest that Wipha will remain a tropical storm and gradually weaken into a tropical depression and eventually a low-pressure cell as it moves into Laos.

He said that based on current models, Wipha's impact on Thailand could be less severe than Yagi's. However, the risk remains high for heavy rainfall, flash floods, and landslides. Models from both the TMD and international weather apps forecast that July 23–24 (Wednesday–Thursday) will be the peak days for heavy rain in Thailand.

"We’ve learned from past experience with Yagi," Thon wrote, "and should be better prepared this time. No need to panic, but we must remain vigilant and act swiftly in the face of any emergency."

He urged the public to keep monitoring storm updates for any changes in intensity or direction.