The hurricane, a Category 1 storm, was about 195 miles west-southwest of Lisbon, Portugal, the National Hurricane Center said in an 11 a.m. advisory on Friday. Leslie's maximum sustained winds were 75 mph (120 kph) and those hurricane-force winds extend outward for 95 kilometers (60 miles).
The exact trajectory of the hurricane, however, remains uncertain due to the presence of another storm approaching the region from the north, Portugal's meteorological institute said.
Storms packing almost 180 kilometres-per-hour winds hit Portugal early Sunday leaving hundreds of thousands of people without power before carrying heavy rain on into Spain, authorities said.
Michael killed at least six people in Florida, Georgia and North Carolina from falling trees and other hurricane-related incidents, officials and local media said.
It will arrive at the central coast Saturday night and continue into Spain as a weaker storm.
Luis Belo Costa of Portugal's National Protection Agency recommended that people "avoid at all costs walking on the street".
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Spanish meteorologists expected Leslie to reach Spanish mainland territory early Sunday before weakening to a tropical storm. The swells are likely to bring "life-threatening surf and rip current conditions".
Hurricanes formed on the American side of the Atlantic rarely bring their destructive force to Europe.
The storm is thought to be the most powerful to hit Portugal since 1842.
Only Hurricane Vince has made landfall on the Iberian peninsula over the last 176 years, hitting southern Spain in 2005, according to weather records.
Leslie first became a sub-tropical storm almost three weeks ago on September 23.