Temperatures Thursday will reach 41C as a result of a low-pressure system over northern Thailand, the Thai Meteorological Department (TMD) says.
The TMD's heat forecast is lower than forecasts by some experts who predict the temperature could reach 42C.
Bangkok temperatures last reached 41C during March in 2012 and 2013. The TMD forecast for the weekend is for daily highs of 34C.
According to the TMD, hot weather will cover the North, the Northeast and parts of the Central Plains, Thursday. The hottest region will be the Northeast.
TMD director-general Wanchai Sakudomchai said Wednesday that high temperatures resulted from low-pressure systems and the sun's rays striking the country at a perpendicular angle.
He rejected claims that a heatwave from the Pacific Ocean could hit the country.
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Earlier, Jirapol Sinthunava, a professor at Mahidol University's Faculty of Environment and Resource Studies said the country might be hit by the heatwave due to hot air masses from the Pacific Ocean.
Meanwhile, Anond Snidvongs, executive director of the Geo-Informatics and Space Technology Development Agency, said it was less likely that Bangkok would be affected by today's extreme temperatures as the city was located close to the Gulf of Thailand.
Permanent secretary for public health Sophon Mekthon Wednesday warned the public, especially children, the elderly and those who work outdoors, to watch out for heat stroke as temperatures surge between 11am and 2pm today.
