Strong winds and heavy rain are forecast to batter Britain as Storm Agnes, the first named storm of the season, sweeps across the country.
Agnes will first hit western regions of the UK and Ireland on Wednesday, with the most powerful winds expected on the Irish Sea coasts.
All of Scotland, Wales and Northern Ireland are under the warning from noon on Wednesday until 7am on Thursday.
Large parts of Northern England, the East Midlands, South-west England counties and Oxfordshire are also on alert from the same time.
The Met Office warning reads: “A deep area of low pressure named Storm Agnes is expected to approach south-west Ireland early on Wednesday and track across northern parts of the UK before clearing early [on] Thursday.
“There is some uncertainty on the precise track and depth of the low, however, the most likely outcome at present is, for a wide swath, 80 to 95kph gusts to affect inland areas, perhaps locally stronger over and to the lee of hills in the north.”
Ireland has warned small boats that wind speeds will reach force seven or higher.
Agnes is a remnant from a system named Tropical Storm Ophelia by US weather officials that brought heavy rain and wind to parts of east coast America last weekend.
Agnes will maintain strong winds as it crosses the UK on Wednesday and into Thursday.
Scotland, Wales, Northern Ireland and northern England will also be hit by heavy rain, with the possibility of up to 60mm in high-altitude areas of Scotland.
Met Office chief meteorologist Steve Ramsdale said: “Exposed coastal areas could see gusts of 100-120kph with a small chance of a few places seeing around 130kph.”
Storm Agnes will bring some heavy rain, with the highest totals more likely in Scotland, northern England, Wales and Northern Ireland. About 60mm of rain could fall over high ground in Scotland.
Met Office spokesman Stephen Dixon said: “The west of Wales could see about 20mm of rain and towards the south-west [of the UK] a little bit less, but these showers could be fairly heavy in nature. Northern Ireland could see an excess of 30mm of rainfall in a relatively short period of time.”
Forecasters have warned of the potential for some damage to buildings from strong winds, as well as the possibility of power cuts.
Transport disruption is expected, with some roads and bridges likely to close.