Storm Ali - the first of the autumn - is forecast to batter a swathe of central Scotland tomorrow with winds up to 80mph.
The Met Office today raised its severe weather warning from yellow - "be aware" - to its second highest level, amber - "be prepared”.
It said “dangerous conditions” were likely.
The warning covers most of Scotland south from Mull and Aberdeen, including Edinburgh and Glasgow. It will be in force from 8am to 5pm tomorrow.
Gusts of 65-75mph are expected across the area, with 80mph possible in exposed locations, such as on coasts and high ground.
The rest of Scotland remains covered by a yellow warning from 6am to 10pm.
The Met Office issued its standard warning for amber alerts that flying debris “could lead to injuries or danger to life”. Building damage was probable, such as tiles blown from roofs or falling trees and branches. It said longer journey times and cancellations were likely as road, rail, air and ferry services may be affected, with some roads and bridges were likely to close. Power cuts may occur, which could affect mobile phone coverage. Large waves could affect coastal roads, sea fronts and homes.
Likely transport disruption could see the year-old Queensferry Crossing closed to lorries and other high-sided vehicles for the first time.
Operator Amey tweeted: “Latest forecast predicts very strong winds gusting up to 76mph at the Forth Bridges on Wednesday afternoon.
“This would see Forth Road Bridge close completely and the Queensferry Crossing close to high sided vehicles for the first time.”
Met Office Chief forecaster Laura Paterson said: “As this is the first spell of very strong winds of the season, and given that most trees are still in full leaf, we are likely to see some dangerous conditions with falling trees and flying branches and other debris likely.
“Strong winds will be accompanied by heavy, squally showers.”
A spokeswoman for the agency said: "Storm Ali will bring a spell of very strong winds to Northern Ireland from early on Wednesday morning, before these strong winds spread to far north west England and central and southern Scotland by late morning.
"Strong winds will be accompanied by heavy squally showers.
"Some areas, especially high ground and coastal regions, including within the Central Belt, could see gusts of 80mph at times.
"Winds will ease from the west through the afternoon.
“The outlook for the remainder of the week is rather unsettled, with further strong winds and heavy rain expected across most parts of the UK.”
Road maintenance firm Scotland TranServ, which covers western Scotland, said it had chainsaws at the ready.
Network Rail Scotland issued a plea to people living beside rail lines to tie down gazebos and trampolines to prevent them being blown onto tracks.
Transport secretary Michael Matheson said: “There is the potential for disruption on the roads, especially on bridges, and people should check the latest information before they set off, drive to the conditions and follow police advice.
“The conditions are also likely to lead to disruption on other modes of transport, so we are urging people to take the weather into account if they are planning to travel on trains, ferries and flights.
“The Scottish Government’s Resilience Room will also be active throughout Wednesday to monitor wider impacts of Storm Ali and to work with partners in helping co-ordinate the response to any issues that might emerge.”