Most of the country will start Tuesday with sunshine, but showers and thunderstorms may develop later as temperatures climb to 27°C to 32°C.
A yellow heat warning remains in force until Wednesday across the country, except along the coast.
The southeast could see a shower or thunderstorm as early as the morning. Elsewhere, cloud will increase through the afternoon, bringing a risk of showers, some of them thundery.
The chance of rain will be lower along the coast. In the northeast, temperatures could locally reach 33°C or 34°C.
This evening and overnight, skies will stay partly cloudy, with a few showers still possible, mainly in central and eastern areas. Some of these could also be thundery. Overnight lows will range from 16°C to 20°C.
Wednesday will be unsettled, with a few light showers still possible in places. Maximum temperatures will fall to between 24°C and 27°C, while winds could become fairly strong at the coast.
Thursday will begin fairly sunny, but cloud will increase from the west later in the day. Conditions should remain largely dry, with temperatures between 19°C and 24°C.
Friday will bring similar temperatures, with some rain still possible in the north. The weekend is expected to turn warmer again and should stay largely dry, according to the institute.
