The Met Office said Scotland and north east England would be battered by wind and rain on Friday.
The first named storm of the season, Storm Otto, is battering parts of Scotland and England.
The Met Office said winds would reach speeds of 60-70 mph – as high as 80mph on exposed coasts in northern Scotland.
A yellow warning has been issued from 03:00 to 15:00 for almost all Scotland and another from 05:00 to 14:00 for the Borders and north east England.
Potential impacts include large waves on North Sea coasts as well as a chance of some damage to buildings
Ferry operator CalMac warned customers of disruption to services between Scotland’s west coast mainland and islands.
Network Rail Scotland said speed restrictions could be imposed on some routes.
Electricity company SSEN said the worst of the weather was expected to hit the Caithness, Orkney and the Western Isles.
More than 130,000 customers on its priority services register have been contacted with storm advice.
The Mountain Weather Information Service described it as a powerful Atlantic storm, warning that upland areas from Scotland to the Pennines could see gusts of up to 100mph.
Met Office chief meteorologist Andy Page said: “Storm Otto will bring high winds and rain to the UK, with some northern parts of Scotland and the northeast of England likely to get the strongest gusts of wind, possibly in excess of 75mph.
“There’s a chance of travel disruption and high-sided vehicles could be particularly prone.
“There’s associated rain with Storm Otto, with 40-50mm likely to fall over parts of western Scotland.”
The storm was named Otto by the Danish Met Office. The UK Met Office has adopted the same name.
It is the first named storm to hit the UK since Franklin last February.
The Met Office’s season for named storms runs from September to September, and the names are given to raise awareness of severe weather.
Earlier this month, flights and ferry services in the Highlands and Western Isles were disrupted by 75mph winds.