Meteorological Department Releases 2025 Monsoon Timeline: When Heavy Rains Expected, When Dry Spells Likely
Thailand's monsoon season began May 15 with overall rainfall expected 10% below normal, though heavy rains are forecast for August-September with risks of flash floods and flooding across multiple regions.
The Thai Meteorological Department officially declared the start of the 2025 monsoon season on May 15, 2025, after confirming that meteorological conditions met Thailand's monsoon criteria: northern Thailand experiencing rain coverage exceeding 60% of the area, lower-level winds shifting to southwestern direction, and upper-level winds changing to easterly winds. The northern monsoon season will continue until approximately mid-October, while the eastern Gulf coast will maintain continuous rainfall through December.
Overall, this year's total rainfall nationwide is expected to be lower than 2024 and approximately 10% below normal. From mid-May to mid-June, rainfall will increase and become more consistent, particularly in the eastern and southwestern coastal regions where heavy rain is possible. Late June through early July will see reduced rainfall and distribution, creating dry spell risks in many areas, especially outside irrigation zones. Rain will return with intensity in August through September, a period requiring vigilance against heavy downpours, flash floods, flash flooding, and riverbank overflows in multiple areas.
**2025 Monsoon Timeline:**
**1. Mid-May to Mid-June** - Increasing and continuous rainfall - Rain covering 40-60% of areas - Eastern and southwestern coastal regions: 60-80% coverage with heavy to very heavy rain in some places
**2. Late June to Early July** - Reduced rainfall volume and distribution - Potential water shortage in some areas, particularly outside irrigation zones
**3. August to September** - Rain covering 60-80% of areas - Heavy rainfall in multiple locations - Very heavy rain in some areas - Risk of flash floods, flash flooding, and riverbank overflows
**4. October** - Northern and northeastern regions: declining rainfall - Cool mornings starting, especially in upper regions - Central, eastern, and southern areas: continued rainfall with heavy to very heavy rain in some areas
The latter half of the year shows a trend toward El Niño conditions. The Meteorological Department is closely monitoring ENSO (El Niño-Southern Oscillation) phenomena, currently in neutral status but with indications of shifting toward El Niño in the second half, potentially resulting in below-normal rainfall and slightly above-normal temperatures for Thailand.
Despite overall lower annual rainfall, vigilance is necessary against periodic heavy rains from monsoon and low-pressure systems, which may cause flash floods, flooding, and agricultural impacts across multiple regions. Tropical cyclone activity is expected to bring one to two systems impacting or affecting Thailand, likely occurring between August and September, primarily affecting northern and northeastern regions.
The Meteorological Department will continuously monitor conditions and issue weather warnings, urging the public to follow forecasts and alerts closely throughout the monsoon season.
