Temperatures in the Thoen district of the northern Lampang province reached 42 degrees Celsius on Monday and Tuesday, the hottest temperatures for this year's summer so far.
Meanwhile, the Meteorological Department said the temperature of Muang district was not far behind at 41.8C.
Temperatures in Lampang surged above 40C from March 28 and did so for six consecutive days.
The department forecasts that Lampang will experience the hottest temperatures this month, with the average temperature ranging from 38C to 40C.
The department also compared the temperature in April during the past five years with the temperature in Lampang's Thoen district, once reaching 44.2C, the highest temperature ever recorded in Thailand.
The department forecasts that the weather in the upper part of Thailand will be hot, blanketing the region until April 8. Thunderstorms with strong winds are also expected as southern and southwestern winds cover the region.
Until next Monday, thunderstorms are also expected in the South as the northwestern wind prevails over the Andaman Sea and the southeastern wind also prevails in the Gulf of Thailand.
The department expects the temperature rise in the North to range from 38C to 44C, while the Northeast will range from 36C to 43C.
The temperature in Central regions is expected to rise between 35C and 44C, while the temperature in the East will be between 33C and 41C.
In Bangkok and its adjacent provinces, the temperature will range from 34C to 41C until Monday.