Thailand is still dealing with widespread flooding after repeated rounds of heavy rain since September 16, while another spell of unsettled weather is expected to bring heavy to very heavy rainfall to parts of the country from October 4.
The latest forecasts raise the possibility of renewed flash flooding and worsening conditions in areas where water levels have only recently begun to fall.
Flooding spreads across Thailand
The current flood disaster began in mid-September as heavy rainfall affected large parts of Thailand.
By September 28, flooding had affected 41 provinces, with more than 2.5 million people impacted, according to the International Federation of Red Cross and Red Crescent Societies. Flooding remained active across 28 provinces, particularly in central and eastern Thailand and around Bangkok.
Bangkok became one of the main centres of the disaster after exceptionally heavy rainfall inundated large parts of the capital.
Nearly 300 mm (11.8 in) of rain fell in Bangkok over 48 hours during the September 25–27 period. Floodwaters covered major roads, entered homes and disrupted transport, while thousands of residents moved into temporary shelters.
By September 29, officials reported that at least 23 people had died in Thailand since September 16. Bangkok had received around 320 mm (12.6 in) of rain over three days, close to the city’s typical September rainfall for the entire month.
Floodwaters are slowly receding
Rainfall has eased in some areas, allowing drainage operations to make progress.
Thailand’s government said on October 2 that the overall flood situation was beginning to improve, with authorities continuing relief and recovery operations in the worst-affected areas.
However, the flood threat has not disappeared.
Water levels remain elevated in several river and canal systems, while accumulated rainfall and saturated ground mean that relatively short periods of intense rain can produce rapid runoff.
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Thailand’s Meteorological Department recorded persistent flooding during the September 25 to October 1 period, particularly across the Central and Eastern regions and Bangkok.
Another round of heavy rain is coming
The next threat is already appearing on the forecast charts.
The Thai Meteorological Department expects a shift to more unsettled weather from October 4 to 7. Heavy to very heavy rainfall is forecast first across parts of northern and northeastern Thailand, before spreading toward the Central region, Bangkok and the East on October 5–6.
The department is warning that accumulated rainfall could trigger flash floods, runoff from higher terrain and overflows, particularly around waterways, foothills and low-lying areas.
The forecast also extends the risk beyond the immediate four-day period. Further heavy to very heavy rain is possible across eastern and southern Thailand on October 8–9.
Monsoon moisture meets changing winds
The recent flooding has been driven by a combination of persistent monsoonal moisture, an active monsoon trough and low-pressure systems moving across the country.
During September 25–October 1, the monsoon trough stretched across lower central and eastern Thailand while an active low-pressure area moved from the East across the Central region and Bangkok before continuing westward toward Myanmar.
Bangkok flooding be like…
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At the same time, a relatively strong southwest monsoon supplied additional moisture from the Andaman Sea and surrounding waters.
The combination produced widespread heavy and very heavy rainfall across central and eastern Thailand, with rainfall accumulating faster than drainage systems could remove it.
The next weather change has a slightly different setup.
The Thai Meteorological Department expects a high-pressure system from China to extend into northern Thailand and the upper Northeast from October 4. This will interact with the prevailing southwest monsoon, helping destabilize the atmosphere and generate thunderstorms, gusty winds and locally intense rainfall.
A fragile recovery
The timing is particularly important because the ground and waterways have not fully recovered from the previous rainfall.
Even as floodwaters retreat from some urban areas, saturated soils and elevated river and canal levels leave little capacity to absorb another substantial rainfall event.
That means the next round of thunderstorms does not need to reproduce September’s rainfall totals to cause new problems.
For Bangkok and surrounding areas, the most significant period currently highlighted by the Thai Meteorological Department is October 5–6. Elsewhere, the focus will shift between northern, northeastern, central and eastern Thailand as the weather pattern evolves.
With additional heavy rain possible into October 9, Thailand’s flood emergency is therefore entering another critical phase just as the first signs of recovery are emerging.
