Electricity demand surged to a new high of 35,830 megawatts at 8.58pm on Monday when temperatures nationwide averaged 35-38C, with a peak temperature of 42C recorded the same day, say energy officials.
The demand surpassed the previous record of 34,656MW set on the evening of April 6.
The protracted hot spell has resulted in power consumption records being set and broken eight times since Feb 22, when demand of 30,989MW first broke the previous year's record, say energy officials.
Electricity consumption in Thailand is usually less than 30,000MW, outside the hot and dry season.
The Energy Policy and Planning Office earlier estimated that demand peaks this year would exceed 35,000MW because of the effects of the El Niño weather phenomenon.
This cyclical phenomenon causes the oceans to heat up, increasing temperatures and bringing drought to many countries.
The Meteorological Department reported on Monday that it expects the extremely hot weather in the North, the Northeast, central plains and the East to last until Sunday.
A low-pressure system is forecast to remain over these regions until April 28, causing the weather to be very hot and overcast.
Temperatures could reach 43°C in the North, 42C in the central plains, 41C in Greater Bangkok, the Northeast and the East, and 40C in the South, the department said.
Officials advised people to refrain from extended outdoor activities if possible.
The sun will be at its zenith over Bangkok, directly above it as it migrates north, at 12.16pm on Friday, according to the National Astronomical Research Institute of Thailand.
The hot weather was among the factors driving up the Thai Industry Sentiment Index to 92.4 points in March, from 90 in February, according to a report by the Federation of Thai Industries (FTI).
Kriengkrai Thiennukul, chairman of the FTI, attributed the increase partly to people buying more household appliances and furniture.
Air conditioners have recorded healthy sales this year because the weather is so hot, he said.