Prepare for another round of rain from 18–20 September 2026 before winter arrives mid-October. This year is expected to have fewer coldest days than last year, only 2–3 days, due to the super El Niño effect.
Today (18 September 2026), the Meteorological Department issued a warning for 18–20 September 2026 to beware of heavy to very heavy rain and accumulated rainfall that may cause flash floods and forest runoff, especially in foothill areas near waterways and low-lying zones. Small boats in the upper Andaman Sea should refrain from sailing during this period. Other areas should navigate cautiously and avoid thunderstorm zones.
This period is nearing the end of the rainy season and the transition to winter. Thairath Online's special team consulted a source from the Meteorological Department who stated that from 18–20 September 2026, heavy rain is expected, especially in the western southern region including Ranong, Phang Nga, Krabi, and Phuket. The monsoon is still active, with southern winds bringing some cool air, but it is moist and not yet distinctly cold. This causes a rain trough to pass through central parts of the country, resulting in continuous rain in the lower northern region, northeastern, central, and eastern regions. Rainfall is expected to decrease around 21–22 September 2026.
Cold winds have started to arrive intermittently but currently clash with rainy winds, so their presence is not yet clear. The cold air will take over once the rainy winds weaken, which requires a shift in wind direction and temperature drop. At present, wind directions remain unstable. Cold air is expected to arrive around mid-October 2026. When wind patterns stabilize, the official start of winter will be declared.
The winter season of 2026 will have fewer cold days compared to last year, which had about 3–5 cold days. This year, cold days are expected to reduce to only 2–3. Average temperatures will be higher than the usual winter seasons. The cold spells will be brief and intermittent, quickly followed by warmer periods. However, there will still be days with cool weather, mainly experienced in highland or mountain summit areas.