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Thailand Weather Alert: July 11, 2026 — Rough Seas and Heavy Rain Nationwide
The Thai Meteorological Department (TMD) has issued a significant weather advisory for July 11, covering dangerous sea conditions across the Andaman Sea and Gulf of Thailand, along with heavy rain affecting most of Thailand. A combination of a low pressure system over upper Vietnam and a strengthening southwest monsoon is driving the rough conditions. While Typhoon Bavi is active over the Pacific northeast of Taiwan and expected to make landfall on China's east coast on July 11-12, the TMD has confirmed it will not track into Thailand directly. That said, it is amplifying monsoon intensity across the country.
Sea Conditions Around Koh Lanta
For visitors on or near Koh Lanta, conditions are rough. The area falls under the southern west coast zone (Krabi southward), where winds are running at 20-40 kph and waves are reaching 2-3 metres, with heights above 3 metres during thunderstorms. Waves are breaking onshore along the Andaman west coast, making beach activities genuinely dangerous.
Further north toward Phuket, conditions are even more severe, with waves of 2-4 metres and gusts pushing waves above 4 metres in storms.
Boat and Ferry Warning
The TMD has advised all small boats in the Andaman Sea to stay ashore until at least July 15. That covers the full stretch from Phuket down through Krabi and Koh Lanta to the southern islands. Boat trips, speedboat transfers, and island-hopping around the Andaman are high-risk until that date. Sailors are also warned to avoid any areas where thunderstorms are active.
Rain Forecast Across Thailand
Thunderstorm coverage of around 60% is expected across most of the country. Here is how conditions break down by region:
<table> <thead> <tr> <th>Region</th> <th>Heavy Rain Areas</th> <th>Temperatures</th> </tr> </thead> <tbody> <tr> <td>North</td> <td>Mae Hong Son, Chiang Mai, Chiang Rai, Phayao, Nan, Tak</td> <td>22-32 C</td> </tr> <tr> <td>Northeast</td> <td>Nong Khai, Bueng Kan, Sakon Nakhon, Nakhon Phanom</td> <td>23-34 C</td> </tr> <tr> <td>Central</td> <td>Uthai Thani, Nakhon Sawan, Lop Buri, Saraburi, Kanchanaburi, Ratchaburi</td> <td>23-36 C</td> </tr> <tr> <td>East</td> <td>Chanthaburi, Trat</td> <td>25-35 C (winds 20-40 kph)</td> </tr> <tr> <td>South West Coast (40%)</td> <td>Ranong, Phang Nga</td> <td>23-34 C</td> </tr> <tr> <td>South East Coast (30%)</td> <td>Prachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat</td> <td>23-37 C</td> </tr> <tr> <td>Bangkok (60%)</td> <td>Mainly afternoon and evening storms</td> <td>26-36 C (winds 10-25 kph)</td> </tr> </tbody> </table>
Hazard Warnings
Beyond the sea, the TMD flags flash flood and runoff risk in low-lying areas, particularly near slopes and waterways. If you are staying anywhere close to a hillside or stream, keep an eye on conditions throughout the day.
What This Means for Your Plans
If you are based in Bangkok, Chiang Mai, or on Thailand's east coast near Pattaya or Phuket, the main concern is afternoon thunderstorms rather than sea hazards. Plan outdoor activities for the morning where possible.
For anyone on Koh Lanta or elsewhere along the Andaman coast, skip the boat trips and stay well back from the shoreline. The July 11-15 window is a genuine rough patch, and conditions can shift quickly during thunderstorms. Inland sightseeing is a reasonable alternative while the weather settles.
Information sourced from The Thaiger.