Architects working on the preservation of Notre-Dame rush to cover the cathedral before the rain can cause further damage.
On Tuesday evening, showers and possibly thunderstorms are predicted in the French capital.
vault of the cathedral collapsed in the fire, is already partially sullied after the firefighting measures.
Architects fear that heavy rainfall could lead to another collapse.
The emergency plan was "the highest priority".
"The beams are here, the tarpaulin is coming in. The climbers, as there will be climbers, and the scaffolders are ready," he said.
It is already planned to erect a large, purpose built "umbrella" on the roof of the landmark, which will have its own summit and protect the structure while reconstruction takes place.
But the umbrella is not finished yet – and the threat of rain is too serious to wait, with even stronger rain forecast for Thursday.
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The old cathedral was completely destroyed during the heavy fire on April 15. The firefighters managed to save the structure and much of their interior – however, emergency measures were taken to stabilize the building.
Three large holes in the vault of the cathedral – the vaulted ceiling – are the most obvious signs of damage. One was made by the collapse of the spire of the cathedral.
But their famous rose-stained-glass windows were covered with protective material and reinforced with wooden posts.
What's next for Notre-Dame?
French President Emmanuel Macron has vowed to rebuild the symbol of Paris within five years – in time for the city's Olympic Games planned for 2024.
The costs are likely to be enormous. Hundreds of millions of people have already been pledged by individuals and businesses in France and France from around the world.
Prime Minister Édouard Philippe has proposed an international competition for designs for the new lace to replace the 19th-century design by Eugene Viollet-le-Duc, who collapsed.
In the meantime, however, it is planned to build a temporary wooden cathedral in the square outside to continue the Catholic worship services on the site. The idea that had already earned the approval of the Paris Mayor Anne Hidalgo.
Notre Dame was already extensively expanded when the fire broke out. It is not yet clear if this contributed to the fire or what the cause was.
In addition to protecting the cathedral from the rain, removing the damaged scaffolding is one of the first steps towards complete restoration of the cathedral – a process that could take weeks.