The Met Office on Thursday predicted that the heatwave may continue for three more days.
It was the third consecutive extension.
At least four people died of heatstroke one each in Chattogram, Kurigram, Chapainawabganj and Noakhali on Thursday.
The toll rose to 29 since April 19.
Weatherman Md Shaheenul Islam issued the heatwave warning, effective from 9:00 am on Thursday.
He forecast that the heatwave might continue throughout the rest of April.
On Thursday, 42.4 degrees Celsius the highest for the country was recorded in Jashore, while the lowest temperature of 17.7 degrees Celsius was recorded in Tetulia.
In Dhaka division, 41 degrees Celsius, the highest was recorded in Faridpur, and 24.6 degrees Celsius, the lowest was recorded in Nikli.
According to the Met Offices latest bulletin, Sylhet division might witness rains or thunder showers accompanied by temporary gusty or squally winds, with isolated hailstorms on Friday.
The Met Office forecast predominantly dry weather with occasional partly cloudy skies and minimal fluctuations in both day and night temperatures due to increased moisture incursion on Friday.
The discomforts may persist.
The Met Office forecast that the heatwave may continue till Saturday, with the possibility of rains or thunder showers accompanied by temporary gusty or squally winds in one or two places in Sylhet division, along with isolated hailstorms.
Elsewhere in the country, predominantly dry weather with temporary partly cloudy skies are expected.
On Monday, the Met Office said that the heatwave may continue till Wednesday.
After the Eid Vacation, Schools, colleges and madrassas were closed for seven days, since April 21, due to the heatwave.
The authorities announced that schools, colleges and madrassas will reopen on Sunday.
