Weathermen warn that temperatures could hit new highs between Friday and Tuesday, with the wet season not due to start until the third week of May.
The Meteorological Department said on Wednesday morning that the heat wave would continue through Wednesday and Thursday.
From Friday through to Tuesday next week, westerly and northwesterly winds would reach the North, Northeast, Central Plain and the East, with high temperatures that could break records set in 2016 and 2023.
A record 44.6°C was measured in Mae Hong Son province on April 28, 2016, and again in Tak province on April 15, 2023.
This year's high to date is 44.2°C, in Lampang on Monday this week.
Along with the extremely hot weather, demand for electricity set a new high on Monday night of 35,830 megawatts.
