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Flash Floods and Heavy Rain Warning for Thailand: September 23-27, 2026
The Thai Meteorological Department (TMD) has issued a warning covering September 23-27, 2026, flagging flash floods and heavy run-off as a real risk across large parts of the country. A strong low-pressure area over the coast of central Vietnam is moving across the lower Northeast, East, and Central Thailand (including Bangkok), running along a monsoon trough over upper Thailand. This is being reinforced by a strengthening southwest monsoon over the Andaman Sea, Thailand, and the Gulf of Thailand. If you're travelling in Thailand this week, including Koh Lanta and the wider Andaman coast, it's worth building some flexibility into your plans and keeping an eye on official updates.
What's Causing It
The warning was published on September 23, 2026 at 9:27 AM, written by Chattarin Siradakul and reviewed by Ryan Turner, English News Editor. According to TMD, the system will move through the country in stages: the lower Northeast and East get hit first, then it spreads to the North and Central Thailand (including Bangkok and surrounding provinces), before reaching the South. The main concern is flash floods and sudden run-off, particularly near foothills, waterways, and low-lying areas.
Where and When
<table> <tr><th>Date range</th><th>Areas affected</th><th>Main risk</th></tr> <tr><td>Sept 23-27, 2026</td><td>Lower Northeast, East</td><td>Heavy rain, flash floods (first to be affected)</td></tr> <tr><td>Sept 23-27, 2026</td><td>North, Central Thailand, Bangkok and surrounding provinces</td><td>Heavy rain expected in many areas, very heavy rain possible in some locations</td></tr> <tr><td>Sept 23-27, 2026</td><td>South</td><td>Spreads here after the North and Central regions</td></tr> </table>
Sea Conditions and Small Boat Advisory
Conditions at sea are also worsening:
<table> <tr><th>Area</th><th>Wave height</th></tr> <tr><td>Upper Gulf of Thailand</td><td>2-3 m, could exceed 3 m during thunderstorms</td></tr> <tr><td>Lower Gulf of Thailand and upper Andaman Sea</td><td>Around 2 m, could exceed 2 m during thunderstorms</td></tr> </table>
Small boats in the upper Gulf of Thailand have been told to stay ashore from September 24-27, 2026.
What This Means for Tourists
If you're in Bangkok, Central Thailand, the lower Northeast, East, or later the North and South, expect heavy to very heavy rain through September 23-27, 2026, with a genuine risk of flash flooding and sudden run-off. A few practical points:
- Avoid roads known to flood, especially low-lying routes, during this period.
- During thunderstorms and lightning, stay away from open areas, large trees, unstable structures, and loose signage.
- Sea conditions will worsen, with waves of 2-3+ m in the Gulf of Thailand and around 2+ m in the Andaman Sea. Boat trips, ferries, and water activities carry elevated risk.
- Build some flexibility into your itinerary if you're in an affected province, and check official TMD updates before heading out.
TMD can be reached via their website or 24-hour hotlines 02-399-4012-13 and 1182.
Related Reports
TMD had already flagged heavy rain for 21 provinces on August 14, 2026, and issued another heavy rain report roughly three weeks before this latest warning, covering Bangkok and surrounding provinces. Other recent flooding news includes Phang Nga floods affecting around 1,000 households in Takua Pa, and a flash flood at Mae Sa Waterfall in Chiang Mai that swept away a tourist.
Information sourced from The Thaiger.