Yellow "be aware" warnings are also in place for Scotland for Wednesday to Saturday.
The Met Office said a storm, named Storm Barbara, could see winds gusting to 90mph over western and northern parts of Scotland.
Forecasters have warned of possible disruption to power supplies.
The amber warning is in place from 12:00 Friday to 06:00 Saturday.
The Met Office said: "A spell of very strong south to southwesterly winds is expected to develop on Friday.
"Gusts of 80mph are likely quite widely, with westerly winds gusting to 90mph likely across parts of western and northern Scotland later on Friday and overnight into Saturday.
"Winds will then ease on Saturday morning."
It added: "Be aware of the potential for some structural damage - this more likely across the northwest of the warning area - as well as disruption to power supplies and travel, with restrictions on bridges and disruption to ferries."
Shetland is likely to be the last place to see winds easing on Saturday, the Met Office said.
The yellow warnings warns of winds gusting to up to 55mph on Wednesday to Thursday and to 70mph on Friday and Saturday.
Snowfalls with accumulations of five to 10cm have also been forecast upland areas of western and central Highlands.
Ferry operator Caledonian MacBrayne has said 21 of its 26 routes have already been disrupted by the weather. Several services have been cancelled.
Western Isles Council - Comhairle nan Eilean Siar - has shut the Braighe, the causeway to Point on Lewis, because of strong winds and high tides.

8 March 2016 Last updated at 17:25 GMT
Despite equal pay legislation being introduced in 1970 a gender pay gap still exists today. According to the Office of National Statistics, women are still paid 24.6% less than their male counterparts in skilled trades.
Video produced by BBC Rewind

But they say it is still too early to say whether it is the remains of Swedish journalist Kim Wall.
She was last seen alive on 10 August as she departed on a trip with submarine inventor Peter Madsen.
He initially said he had dropped her off safely near Copenhagen, but has since said she died in an accident and that he had "buried" her at sea.
The body has been sent for DNA analysis, but the results will not be available until Thursday morning.
Divers continue to search the waters near where the torso was discovered, but, despite some reported sightings, other remains have not been found.
"The current situation is that there is a torso in which arms, legs and head have been removed off as a result of deliberate cutting," said Jens Moller Jensen of the Copenhagen police.
"There is nothing about the length of the torso to indicate that it is not Kim Wall, but we do not yet know."
Ms Wall, 30, was a freelance journalist who had graduated from the Columbia Graduate School of Journalism. She was based between New York and Beijing and had written for The Guardian and The New York Times.
She was reported missing by her boyfriend after she failed to return from what should have been a short trip to research a feature about Mr Madsen and his submarine, the Nautilus.
The submarine sank hours after the search for the journalist began, and Mr Madsen was charged with negligent manslaughter. Danish police believe the 40-tonne vessel was deliberately sunk by Mr Madsen, who was rescued before being arrested.
The torso was found on Monday in shallows off the densely populated Danish island of Amager, on which the Danish capital of Copenhagen is partly situated.
Mr Madsen denies any wrongdoing.
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The Met Office has issued an amber "be prepared" weather warning for large parts of Scotland for Friday and Christmas Eve.
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Parity is this year's theme for International Women's Day so 46 years after the introduction of the Equal Pay Act, BBC Rewind looks back on the history of the gender pay gap.
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A headless and limbless corpse found in waters off Denmark was deliberately mutilated, say Copenhagen police.