The Meteorological Department forecast is for extremely hot weather in the North, the Northeast, the Central Plains and the East from Monday to Sunday, with temperatures likely to peak in the North at 43 degrees Celsius on Monday.
The heat is the result of a low pressure zone expected to remain over the North, Northeast, Central and East regions from April 22-28. The weather is expected to be very hot and overcast.
Temperatures could reach 43°C in the North, 42 degrees in the Central Plains, 41 degrees in Greater Bangkok, the Northeast and the East and 40 degrees in the South on Monday, the weather office said.
It advised people to refrain from extended outdoor activities if possible.
Thunderstorms are possible in some areas, brought by southeasterly and southerly winds. Rain was expected in the lower South due to westerly and northwesterly winds over the Andaman Sea and the South, the department said.
The National Astronomical Research Institute of Thailand said on Monday that the Sun would be at its zenith over Bangkok, directly above as it migrates north, at 12.16pm on Friday.
However, Friday would not necessarily be the hottest day in the capital this year. There were other factors involved such as rainfall, cloud cover, monsoon influences and heat accumulation, the institute said.