Heavy rain is expected in the central region and Bangkok from 29 to 31 May, then shifting to heavy rain in the south and east. In June, another wave of heavy rain is anticipated in the northern region.
Mr. Somkuan Tonjan, Director of the Weather Forecast Division and Deputy Spokesperson of the Meteorological Department, said that rain is forecast for the short period from 29 May to early June 2026, with the peak from 29 to 31 May when rain will be most widespread in the upper regions and Bangkok, especially on 29 and 30 May when the heaviest rain is expected.
Bangkok and surrounding areas are expected to have heavy rain over the weekend of 29-30 May, typically forming in the afternoon or evening, which may impact outdoor activities.
From 1 to 4 June, rain will decrease in the upper areas but intensify along the Andaman coast of the south and the eastern region due to strengthening monsoon winds.
Areas at risk of heavy rain include the Andaman coast provinces such as Ranong, Phang Nga, and Phuket, which face the monsoon winds, as well as eastern provinces like Chanthaburi.
Mr. Somkuan observed that the current weather will be hot and humid, differing from April's dry heat, because moisture from rain is present although clouds remain sparse.
The heat is caused by clear skies and few clouds, allowing full sunlight to reach the ground, combined with the sun being nearly overhead in the northern region during May.
This year's rain is unusual, often falling at night because heat builds up in the morning and moves with the monsoon in the afternoon or evening. Additionally, rain falls in "clusters," with some spots experiencing heavy rain while nearby areas remain dry.
From 9 to 13 June, the monsoon trough is expected to become more distinct and shift northward, increasing rainfall in the upper northern and northeastern regions, as well as in Laos and Vietnam.
Flood concerns remain low for major "upper river" floods, but flash flooding may occur in places like Chiang Rai or Mae Sai if continuous rain accumulates over 3-4 days (60-100 mm), as some flood barriers are still incomplete.
Rainfall is below normal; although rain comes in the season, this year lies in the transition phase of El Niño, weakening trade winds and reducing moisture from the South China Sea.
The main concern is drought. Experts worry more about dry spells or inconsistent rainfall than flooding, which could harm farmers growing wet-season rice if rains stop for 7-10 days after planting, potentially damaging the crops.
It is advisable to prepare water sources or storage containers well, as overall rainfall this year is expected to be less than usual.