Thailand issues nationwide flood warning

Thailand's Department of Disaster Prevention and Mitigation issued a nationwide warning on Tuesday night for possible flash floods and forest runoff on Wednesday and Thursday after heavier rain spread across the country. The warning covered Bangkok and followed Thailand's official entry into the wet season on May 15, according to the Bangkok Post. Thailand's Meteorological Department said continuous rain and isolated heavy to very heavy falls were expected through May 21 as a stronger southwest monsoon crossed the Andaman Sea, Thailand and the Gulf. NOAA's Climate Prediction Center said separately last week that El Niño is likely to emerge in May-July 2026. ### Which Thai agencies issued the warning, and what exactly did they say? The Department of Disaster Prevention and Mitigation said the alert was issued because increased rain raised the risk of flash floods and runoff nationwide on Wednesday and Thursday. The Bangkok Post reported that officials told provincial authorities to monitor local conditions, warn residents in vulnerable areas and prepare evacuations where necessary. (bangkokpost.com) The Thai Meteorological Department said in its May 21 forecast that a rather strong southwest monsoon was prevailing over the Andaman Sea, Thailand and the Gulf, while a low-pressure cell covered the lower North and upper Northeast. That setup was expected to bring continuous rainfall and isolated heavy to very heavy rain in the North, Northeast and the South's west coast. ### Which parts of Thailand were under the heaviest-rain threat? (bangkokpost.com) Bangkok Post said meteorologists expected heavy and very heavy rain from Tuesday to Thursday in the North, Northeast, Central Plains and the western coast of the South. The warning included Bangkok, where separate city alerts had already flagged possible flooding along the Chao Phraya River from May 17 to May 21 because of high sea levels and prevailing winds. (tmd.go.th) A Thai Meteorological Department bulletin carried by Thairath listed provinces at risk from heavy to very heavy rain and possible flash floods through May 21. The bulletin said residents near foothills, waterways and low-lying areas should watch for runoff and sudden flooding. ### Why did the warning come now? May 15 marked Thailand's official start of the wet season, according to the Bangkok Post, and the nationwide warning was issued five days later as rainfall intensified. (bangkokpost.com) The Meteorological Department said the immediate driver was the stronger southwest monsoon combined with a low-pressure area over parts of inland Thailand. (en.thairath.co.th) The weather pattern was not limited to one province. Nation Thailand reported on Thursday that the same monsoon flow was still producing widespread thundershowers, with isolated heavy rain in parts of the East, the South's west coast and the Bangkok metropolitan area. ### Where does El Niño fit into this week's flood story? NOAA's Climate Prediction Center said in its latest ENSO Diagnostic Discussion that El Niño is likely to emerge soon, with an 82% chance in May-July 2026 and a 96% chance of persisting into December 2026-February 2027. (bangkokpost.com) That forecast describes a broader climate backdrop rather than the direct cause of Thailand's two-day flood warning, which Thai agencies tied to monsoon conditions and a low-pressure cell. (nationthailand.com) The Bangkok Post learning edition linked the flood alert to the same period in which meteorologists were warning about a fast-developing El Niño. The Thai warning itself, however, focused on immediate rainfall, runoff and local preparedness measures. ### What should residents and travelers watch next? May 21 is the key near-term date in the current Thai weather bulletins, with the Meteorological Department's forecast and heavy-rain alerts updated on its official weather pages. (cpc.ncep.noaa.gov) Provincial authorities were instructed to monitor local conditions and issue evacuation notices if needed, the Bangkok Post said. NOAA's next ENSO updates will come through its regular Climate Prediction Center discussions, while Thailand's next practical signals will be provincial rainfall warnings, river-level alerts and any renewed notices from the Department of Disaster Prevention and Mitigation. (bangkokpost.com) (cpc.ncep.noaa.gov) (tmd.go.th)