Soaring temperatures that show no signs of easing have raised concerns about more deaths from heat stroke, which has already killed 34 people in less than two months.
The Public Health Ministry is closely monitoring conditions as high temperatures have persisted into May, although the Meteorological Department still expects the rainy season to start on May 15.
Heat exhaustion killed 34 people between early March and April 22, according to ministry figures released on Saturday.
Dr Sophon Mekthon, the ministry's permanent secretary, advised people to avoid staying out or doing exercise in the heat for long periods in iorder to prevent heat exhaustion. Those doing outdoor activities should drink one litre of water every hour, even if they don't feel thirsty, to prevent dehydration, he added.
The El Nino effect has contributed to unusually hot weather conditions in Thailand and other countries this year. Forecasters now say that the emerging La Nina phenomenon that usually follows El Nino is likely to bring more rain than usual to much of Asia.
The weather bureau warned on Saturday of extremely hot conditions until Monday in the northern, northeastern, eastern and central regions. Temperatures could rise to 42 degrees Celsius in some areas before summer storms and strong winds arrive from Tuesday to Friday to the upper part of the country, it added.
Sukhothai was the hottest province on Friday at 43.6C, slightly ahead of Nakhon Sawan, at 43.5 and Uttaradit at 43, the department said.