The Thailand Meteorological Department said a heat low-pressure cell will send temperatures soaring as high as 40 degrees centigrade by the end of the week.
People in parts of upper Thailand were warned to watch out for isolated thundershowers and gusty conditions brought by southerly and southeasterly winds.
The South will be drier thanks to a weak easterly wind across the Gulf of Thailand.
Weather forecast for the next 7 days:
North
April 10-14: Hot to very hot days with haze and isolated light rain. Temperature lows of 21-23C and highs of 33-39C.
April 15-16: Hot to very hot with haze, isolated thundershowers and gusty winds.
Lows of 24-26C and highs of 35-40C.
Northeast
April 10-14: Hot with haze and isolated thundershowers. Lows of 22-25C and highs of 32-36C.
April 15-16: Hot with haze with isolated thundershowers and gusty winds. Lows of 23-26C and highs of 34-38C.
Central
Hot and hazy throughout the week, with isolated thundershowers and gusty winds on April 15-16. Lows of 23-27C and highs of 34-39C.
East: Hot and hazy throughout the week, with isolated thundershowers on April 13-16. Lows of 23-27C and highs of 33-38C. Waves less than a metre high rising to a metre during thundershowers.
South (east coast)
Isolated thundershowers throughout the week. Lows of 21-26C, highs of 30-37C. Waves about a metre rising to over 1 metre during thundershowers.
South (west coast)
Isolated thundershowers throughout the week. Lows of 22-27C, highs of 30-37C. Waves about a metre rising to over 1 metre during thundershowers.
Bangkok and surrounding areas: Hot and hazy throughout the week. Isolated thundershowers with gusty winds from April 11-16. Lows of 23-27C and highs of 33-38C.