The 2026 rainy season is expected to see frequent occurrences of the "rain bomb" phenomenon, with Bangkok closely monitoring floodwaters awaiting drainage. Dry spells are anticipated to accelerate heavy downpours.
Mr. Somkuan Tonjan, Director of the Forecast Division and Deputy Spokesperson of the Meteorological Department, stated that, based on statistics and wind direction tracking, this year's rainy season is expected to become clear and officially start in mid-May, around the third week of May, with the period from 12-14 May marking the full onset of the rainy season.
Before the official start of the 2026 rainy season, intermittent rain and dry spells will occur. Weather conditions will fluctuate between hot, sunny days and occasional rainfall. Once the rainy season begins, dry spells are forecast from June to mid-July, as the monsoon trough shifts northward, reducing moisture. These dry spells may be more pronounced than last year.
Additionally, the El Niño phenomenon and related natural changes are in transition from La Niña to El Niño phases. These cycles, previously lasting 5-7 years, now occur every 2-3 years. This year, El Niño is expected to influence rainfall amounts to be below or near normal levels but will not reach "super El Niño" intensity.
The likelihood of "rain bombs," or sudden, intense localized heavy rain, remains high this year due to fluctuating weather between extreme heat, dryness, and humidity, causing atmospheric instability. Especially during dry spells, when moisture encounters hot air, severe thunderstorms can develop more easily than usual. The chance of rain bombs will persist through August and September, then rainfall will return to normal seasonal patterns once humidity saturates the atmosphere.
In 2026, Bangkok remains at risk of heavy rainfall. Currently, rain often falls in northern areas such as Don Mueang, Rangsit, Pathum Thani, and Nonthaburi.
From 14 May onward, as the southwest monsoon strengthens, rain is expected to move more into inner Bangkok during afternoons and evenings. This raises the risk of short-term flooding awaiting drainage, dependent on drainage system efficiency, though prolonged flooding lasting several days is not expected.
The public is urged not to panic over fears of a super El Niño and to listen carefully to information and announcements from the Meteorological Department.
If rainfall this year is below or near normal, water usage plans should be made for activities requiring large amounts of water, considering reserves for next year.
Residents of Bangkok should prepare for traffic disruptions and temporary flooding during heavy rain events.
