Thailand officially enters 2026 rainy season, with below-average rainfall forecast
Thailand — The Thai Meteorological Department has declared the official start of the rainy season, effective May 15th, 2026, with forecasts indicating that overall rainfall will be lower than last year and below the…
Thailand officially entered the 2026 rainy season on May 15, the Thai Meteorological Department said, marking the shift to wet-weather conditions that will affect Phuket and the rest of the country in the months ahead. The department said total rainfall this year is expected to come in below both last year’s level and the long-term average, with the nationwide total projected at about 10% below normal.
The announcement was made by Meteorological Department Director-General Dr. Sukanyanee Yawinyan during a briefing at the Weather Forecast Operations Center in Bangkok. Officials said the season’s onset was confirmed by rain covering more than 60% of northern Thailand, lower-level winds turning southwesterly, and upper-level winds shifting easterly.
Heavy rain expected first, then a possible dry spell
From May 14-18, strong low-pressure activity over the Bay of Bengal combined with a strengthening southwest monsoon is expected to bring heavy to very heavy rain across northern, central, eastern and southern regions.
Rainfall is then forecast to build gradually from mid-May to mid-June, with the east and the west coast of southern Thailand facing a higher chance of heavy downpours. Late June to early July may bring a dry spell, especially in non-irrigated areas.
Conditions are expected to intensify again in August and September, which the department identified as the period with the highest risk of flash floods, landslides and river overflows.
Sea conditions, storm risk and seasonal outlook
In the Andaman Sea, waves are forecast at 2-3 meters and above 3 meters during thunderstorms. Small boats have been advised to remain ashore, while larger vessels were told to proceed with caution.
The department said one to two tropical cyclones may affect Thailand between August and September, particularly in the north and northeast. It is also monitoring neutral ENSO conditions that could shift to El Niño in the second half of the year, a change that may further reduce rainfall and slightly raise temperatures nationwide.
To support seasonal warnings, the department has opened a Heavy Rain and Rough Seas Monitoring Center.
Source: https://thephuketexpress.com/2026/05/15/thailand-officially-enters-2026-rainy-season/
