Thailand enters 2026 rainy season, with less rain and 1–2 storms forecast
Thailand will officially enter the 2026 rainy season on May 15, with rainfall forecast to be around 10% below normal and one to two tropical storms expected to affect the country.
The Thai Meteorological Department (TMD) has announced that Thailand will enter the rainy season on Friday (May 15), after key meteorological conditions met the criteria for the start of the season.
These conditions include rainfall covering more than 60% of upper Thailand, lower-level winds shifting to a south-westerly direction, and upper-level winds changing to easterlies.
The rainy season in upper Thailand is expected to continue until around mid-October, while the east coast of the South is likely to see continuing rainfall until December.
Rainfall expected to be lower than last year
For the 2026 rainy season overall, nationwide rainfall is forecast to be lower than in 2025 and around 10% below the normal average.
From mid-May to mid-June, rainfall is expected to increase and become more continuous, particularly in the East and the west coast of the South, where isolated heavy rain is possible.
However, from late June to early July, rainfall and its distribution may decline, increasing the risk of dry spells in many areas, especially outside irrigation zones.
Rain is then expected to become more widespread again from August to September. During this period, authorities are urging close monitoring for heavy rain, flash floods, forest run-off and overflowing rivers in several areas.
The TMD is also closely monitoring the El Niño–Southern Oscillation, or ENSO. Conditions are currently neutral, but there is a tendency for a shift towards El Niño in the second half of the year. This could result in rainfall being lower than normal and temperatures slightly above average across Thailand.
Although total rainfall for the year is expected to be below normal, the department warned that heavy rain may still occur at times due to the influence of the monsoon and low-pressure systems. These conditions could trigger flash floods, forest run-off and disruption to agricultural areas.
One to two tropical storms may affect Thailand
The TMD forecasts that one to two tropical storms may move into Thailand or affect the country this year. These storms are most likely to occur between August and September, with the North and Northeast expected to be the main areas affected.
The department has also opened a monitoring centre for heavy rain across Thailand and strong waves in the Andaman Sea. The centre will closely track, analyse and assess weather conditions as the country faces a higher risk of heavy to very heavy rain from May 14–18.
During this period, heavy rain is expected in many areas, especially the North, Central Plains, East and South. The conditions are being driven by an intense low-pressure cell over the Bay of Bengal, together with a strengthening south-westerly monsoon.
At the same time, the Andaman Sea and the Gulf of Thailand are expected to experience strong waves. Waves in the Andaman Sea are forecast to reach 2–3 metres, rising to more than 3 metres in thundershower areas.
People in risk-prone areas are advised to watch out for flash floods and forest run-off, particularly those living near foothills and low-lying areas. Mariners should proceed with caution, while small boats in the Andaman Sea are advised to remain ashore during the affected period.
The TMD said it will continue to monitor the situation and issue weather warnings throughout the rainy season. Members of the public are urged to follow official forecasts and weather alerts closely.
