Amber 90mph winds warning for Storm Abigail
The storm - the first to be named by the Met Office - is also now expected to affect the whole of Scotland from the Central Belt north, which is covered by a yellow - “be aware” - alert.
Ferry and other transport disruption are expected along with possible power cuts.
The amber warning area covers the Western Isles and Skye, the west and north coast and Orkney from 9pm until noon tomorrow. The yellow alert zone will be in force from 6pm until 2pm tomorrow.
Ferry operator CalMac said major disruption was expected amid “treacherous” conditions and waves up to 35ft (11m) high.
Sailings already cancelled for today include between Mallaig and Canna, and Mallaig and Armadale on Skye.
Seven routes are on amber alert for possible disruption, including the main Arran route between Ardrossan and Brodick, Skye and North Uist, Oban-Coll-Tiree, and Mull and Iona.
Operations director Drew Collier said: “There is clear warning that major weather-related disruption to ferry services on the Clyde and Hebrides routes is likely.
“The sea conditions we are expecting could well be too treacherous to sail in.”
A Met Office spokesman said: “South-westerly severe gales will develop later on Thursday, increasing storm force for a time as they veer westerly overnight into early Friday.
“Gusts of 70 to 80mph are likely, and perhaps 90mph across exposed locations.”
The Met Office said “conditions will become very unstable leading to heavy, squally showers. Winds will begin to ease and veer more westerly across the Western Isles and the mainland on Friday morning and across the Northern Isles on Friday afternoon.
“Lighting associated will be an additional hazard, whilst large waves may lead to over-topping along some coasts.”
Abigail was one of an A to Z of storm names chosen by the public to raise awareness of severe weather.