"Meteorological Department" issued a statement announcing the start of the "rainy season" for 2026, expecting less rainfall than last year and warning of heavy rain and strong waves at the season's start.
On 14 May 2026, Dr. Sukanyanee Yawichan, Director-General of the Meteorological Department, announced the start of the "rainy season" for Thailand in 2026 and opened a monitoring center for heavy rain over Thailand and strong waves in the Andaman Sea.
The Meteorological Department officially declared Thailand's rainy season starting 15 May 2026, after confirming meteorological criteria for the season's onset were met. These include rainfall covering over 60% of upper Thailand, lower-level winds shifting to southwest, and upper-level winds shifting eastward. The rainy season in upper Thailand will continue until about mid-October, while the eastern southern region will have rain through December.
Overall this year, total rainfall nationwide is expected to be less than in 2025 and about 10% below the normal average. Rainfall will begin increasing and become more continuous from mid-May to mid-June, especially in the eastern region and western southern coast, where heavy rain may occur in some places.
From late June to early July, rainfall amount and distribution may decrease, causing dry spells in many areas, especially outside irrigation zones, before rain becomes frequent again in August to September. This period requires vigilance for heavy rain, flash floods, forest runoff, and river overflows in many areas.
Meanwhile, the department is closely monitoring the El Niño–La Niña phenomenon (ENSO), currently neutral but trending toward El Niño in the year's second half, which may lead to below-normal rainfall and slightly higher temperatures in Thailand.
Although overall annual rainfall tends to be below normal, vigilance is needed for periodic heavy rain from monsoon influences and low-pressure areas, which may cause flash floods, forest runoff, and impact agriculture in various regions.
Regarding tropical cyclones this year, one to two are expected to affect or impact Thailand, likely during August to September, mainly impacting the northern and northeastern regions.
Additionally, the Meteorological Department has opened a center to monitor heavy rain over Thailand and strong waves in the Andaman Sea to closely track, analyze, and assess weather conditions. From 14 to 18 May 2026, heavy to very heavy rain is forecast in many areas, especially northern, central, eastern, and southern regions, due to a strong low-pressure area in the Bay of Bengal combined with intensifying southwest monsoon winds.
At the same time, the Andaman Sea and Gulf of Thailand will experience strong waves, with the Andaman Sea seeing waves 2–3 meters high and over 3 meters where thunderstorms occur. Residents in risk areas should watch for flash floods and forest runoff, particularly in foothill and lowland areas. Mariners should navigate cautiously, and small boats in the Andaman Sea are advised to avoid going out during this period.
The Meteorological Department will continue monitoring and issuing warnings and urges the public to closely follow weather forecasts and alerts throughout this rainy season.
Thanks to the Meteorological Department Facebook page.