Eight of the country's districts, including the capital Lisbon, are on the highest red alert for extreme weather, with Storm Charles expected to reach mainland Portugal on Wednesday morning after passing the island of Madeira late Tuesday.
Wind gusts are expected to reach up to 140 kilometres (85 miles) per hour, the fourth-highest category on a scale of five of hurricane-force winds.
"All those who can should stay at home," Interior Minister Luis Neves told a press conference on Tuesday.
"Don't underestimate the danger and the risks linked with these extreme weather events," Prime Minister Luis Montenegro said.
The second day of the three-day Web Summit, a premier world tech conference, has been cancelled, organisers said.
Forecasts of downpours have raised fears of floods, especially in cities, like those which devastated the Iberian nation in early 2026.
Between January 22 and February 16, Portugal was battered by six successive storms which authorities said left at least seven dead. Some Portuguese media put the toll higher at nearly 20 direct and indirect victims.
The Iberian peninsula is especially exposed to extreme weather patterns, such as heatwaves and periods of heavy rains, supercharged by man-made climate change.