Cold weather will continue to grip the upper part of Thailand until Wednesday, with residents shivering as temperatures hover between 6C and 10C, the Meteorological Department says.
The department also issued a warning Sunday about rough sea conditions in the Gulf of Thailand.
Meteorological staff advised people to put on warm clothes and avoid prolonged exposure to chilly winds and cold rain.
The announcement said that from tomorrow to Wednesday the westerly trough from Myanmar will move to the North and the Northeast of Thailand causing persistent cold spells.
The northeast monsoon across the South and the Gulf of Thailand will intensify with much more rain, as well as isolated heavy thundershowers, likely.
Waves in the gulf are expected to reach 2m to 4m.
People should beware of dangerous surf conditions. All ships should proceed with caution, and small boats should stay ashore from today until Wednesday.
Morning temperatures in several provinces Sunday dropped to 6C.
The department said a high pressure zone covered the Northeast.
Weather conditions will vary with thundershowers and strong winds following the sharp cold spell.
Weather officials said in Bung Kan province in the Northeast the temperature was 11C with strong winds. Villagers living along the Mekong River were advised to keep warm.
In nearby Nong Khai, the temperature was 17C while the temperature in Nakhon Phanom was 19C.
In Loei, weather officials said villagers in Dan Sai, Phu Rua and Na Haeo districts built a bonfire to keep themselves warm. The temperature there varied between 8C and 14C.
The cold weather attracted many tourists to Phu Rua National Park and Phu Kradung National Park in the province.
In Nakhon Ratchasima, Bua Khemma, a grilled chicken vendor at Nakhon Ratchasima municipality market, said her business was badly affected by the cold spell.
"There were only a few customers coming to buy grilled chicken at my stall today," Ms Bua said.
"It's likely people want to stay warm at home during the cold weather."
The temperature in Nakhon Ratchasima was 18C Sunday.
In Nan in the North, meteorologists said the ground temperature was 13C while the temperature on top of mountains in Pua and Bo Klue dropped to 5C.