The department forecast the hottest areas in each region as follows:
The heat index, also known as the “felt air temperature”, combines air temperature and humidity to measure how hot the weather actually feels to the human body.
A 32-41C heat index triggers the “alert” level at which people working outdoors for extended periods can experience heat exhaustion resulting in nausea, headache, muscle ache, and dizziness.
A 41-54C heat index triggers a “warning” level as people working outdoors can suffer heatstroke which comes with more severe symptoms than heat exhaustion.
A heat low covering upper Thailand will result in hot to very hot temperatures and hazy conditions on Wednesday, the TMD said.
Meanwhile, southerly and southeasterly winds prevailing over the lower Northeast and the East will bring isolated thundershowers and gusty winds, it added.
It advised the public to take care of their health and beware of hot and severe weather conditions.
From Thursday to Sunday, a moderate high-pressure system from China will cover upper Thailand, causing summer storms, thunderstorms, gusty winds, isolated hail and lightning strikes in the lower Northeast and the East, said the TMD.