The cool season in Thailand gets underway today, according to the Meteorological Department, adding the cooler weather will last until the end of February.
Bangkok can expect a seasonal low of around 17 degrees Celsius during this period, the department said yesterday.
Department Director-General Chomparee Chompurat said the weather this year on average will be slightly colder than last year.
She said the temperature for the upper zone of the country on the first day of the cool season will drop to 23C.
The upper zone stretches from Ratchaburi, Nakhon Pathom, Bangkok, Chachoengsao, and Sa Kaeo provinces northwards.
At the same time, there will be less rainfall in the upper region, but heavy rain will persist in the South, Ms Chomparee said.
The lowest temperatures in the upper part of the country will average 20-21C which is slightly lower than last year which saw an average low of 21C. However this temperature is still above the seasonal norm of 19.9C, she said.
The lowest temperatures in Bangkok are forecast to be 17-18C and in adjacent provinces 15-16C.
Ms Chomparee said the lowest temperatures in the North and the Northeast would be 8-9C, with Chiang Rai and Nan in the North and Sakon Nakhon and Nakhon Phanom provinces in the Northeast the coldest.
The chilliest time would be from December to late January. It would be extremely cold on mountain tops which will see frost, she said.
In the South, heavy rain will pound the coast from Chumphon southwards.