The Met Office has upgraded its weather warning for Orkney and Shetland to a rare red alert.
It means dangerous conditions are expected with winds set to reach 100mph at times.
A spokesman said: “Storm-force west to south-westerly winds are expected to develop across Shetland during Friday.
Frequent gusts of 80-90mph are expected, with gusts of around 100mph likely for a time this afternoon.
“Additionally, as a result of these winds, very large waves will develop and affect western coasts, during high tide.
“Expect dangerous conditions including structural damage and debris, disruption to power supplies and widespread disruption to transport, and take action to secure loose items.”
Storm force west to southwesterly winds are expected to develop across Shetland during Friday. Frequent gusts of 80-90 mph are expected, with gusts of around 100mph likely for a time this afternoon. Additionally, as a result of these winds, very large waves will develop and affect western coasts, during high tide.
Expect dangerous conditions including structural damage and debris, disruption to power supplies and widespread disruption to transport, and take action to secure loose items.
A rapidly deepening area of low pressure is expected to track close to northern Scotland during Friday. There is now high confidence that Shetland will experience the strongest winds, with gusts quite widely above 90mph and perhaps over 100mph in places. The strongest winds will have peaked by late afternoon, though a yellow warning of wind and snow is valid for Friday night and into Saturday.