Southwestern Germany was already experiencing some of that heat on Friday, with temperatures hitting 32 degrees in the greater Frankfurt am Main area.
Meanwhile the humidity was set to rise in the south and the west, with thunderstorms expected in the area around Munich and spreading eastward later on.
Heavy rain and hail is expected to hit south western Germany between the Eifel mountain range and Munich,reported FOCUS Online.
Flood warnings were issued with up to 40 litres of rain forecast per square metre in places.
In north Germany it will remain hot and dry, with scattered clouds and no threat of rain. It will be windier, as usual, along the coastline.
Heavy thunderstorms will spread by Saturday and are forecast to hit an area from Cologne via Frankfurt to Munich, calming by nightfall and giving way to heavy rain.
Temperatures could then plummet to lows of between 14 and 16 degrees, with 20 degrees forecast overnight in Frankfurt am Main and along the Rhine.
Thunderstorms are also predicted throughout central Germany from North Rhine-Westphalia to Thuringia. But most of the rain will fall down in the south.
South of the Danube will be very wet, with maximum temperatures only reaching 21 to 25 degrees.
Meanwhile dry and hot weather is forecast for the north and east, with temperatures hitting 30 degrees in places over the weekend.
The Sahara in Germany? A heatwave begins
On Monday the rain is set to stop and herald in the start of a new heat wave, with the arrival of hot air from the Sahara desert.
Temperatures will continue to rise and by the end of the week could reach upwards of 35 to 37 degrees.
The highs of 37 degrees are expected on the Upper Rhine, but the 35 degrees mark could also be reached in Hamburg and Berlin.
No end in sight to the drought currently hitting north and eastern parts, with urgently-needed rain not forecast for another ten days.