Authorities have issued a health alert as a heatwave sweeps across many provinces, with the peak "feels like" temperature in Bang Na district of Bangkok forecast to top the table at 50C on Thursday.
The "feels like" or apparent temperature is the temperature equivalent that humans feel, resulting from the combined factors of relative humidity, air temperature and wind speed. In warm climates it is known as the heat index and in cold climates it is called wind chill or chill factor.
Dr Opas Karnkawinpong, permanent secretary for public health, said the intense summer heat could affect people’s health, particularly children, the elderly and those with underlying ailments.
Outdoor workers are at risk of dehydration caused by excessive perspiration and heat exhaustion, he added.
The heat index will be above 40 degrees Celsius in many places on Thursday, with the Meteorological Department predicting a high of 40.6C in Phetchabun, 41.5C in Si Sa Ket, 49.4C in the Laem Chabang area of Chon Buri and 47.9C in Phuket.
Temperatures for record-keeping purposes are taken in the shade, but the heat index or readings in the sun can easily reach 50C in Thailand's hot season. The highest temperature ever officially recorded in the country was 44.6C, in Muang district of Mae Hong Son on April 28, 2016. That broke the previous record of 44.5°C, set in Uttaradit on April 27, 1960.
The heat index in Bang Na on Wednesday reached 45.5C, making it the country’s second hottest spot, after Chon Buri which registered 45.8C. There was also no escaping the sweltering conditions in Phangnga (43.3C), Tak (41C) and Si Sa Ket (38.4C).
April typically is the hottest month of the year.
Dr Opas said the most serious condition may develop in the form heat stroke if a person is exposed to heat for too long.
Heat of 41C or above is dangerous as it can trigger cramps in the legs, abdomen or shoulders, as well as spasms and even heat stroke, he said.
He advised people to drink plenty of water at regular intervals and not wait until they feel thirsty before drinking.
Also, Dr Opas recommends avoiding tea, coffee, fizzy drinks and alcohol as well as spending too much time outdoors.