The cold season is expected to arrive after the downpour forecast for early next week, with temperatures initially dropping by 2-5°C, the Meteorological Department says.
For the next three days of what the department called the "variable weather conditions" period from Oct 21-26, the upper part of the country will experience rain and strong winds. After that, it will be cold-season time, the department said on Friday morning.
These weather conditions are the result of a clash between a high pressure zone from China, which will bring cooler temperatures, and the present humid and hot weather in Thailand.
Provinces in the currently flooded Central Plains, including Bangkok, are expected to see a significant seasonal change on Oct 22-23.
After the transitional six-day period, the North, Northeast and Central Plains will have less rainfall, but in the South it will get wetter, the department said.