In Lewis, Orkney, Sutherland and Caithness there is the potential for gusts as high as 60 or 70mph, and people are being warned to expect travel disruption, damage to buildings and power cuts.
The yellow warning in Scotland is for wind and runs from midday on Christmas Eve until 3am on Christmas Day.
There is a chance of damage to buildings, injuries from flying debris, and power cuts.
The warning for the Midlands and North East is also for wind and urges people to prepare for “gusty” conditions and possible travel disruption. It finishes at 10pm on Christmas Eve.
Christmas getaway plans have already been hampered by Storm Pia.
In Wales, the warning is for rain, and the flooding of homes and businesses is described as “possible”, finishing at 6pm on Sunday.
The unsettled conditions make a white Christmas more likely, the Met Office has said, particularly over high ground in the far north of Scotland.
However, “picture postcard snowy scenes” are not expected on Christmas Day, said Met Office spokesman Oli Claydon.
A white Christmas is defined as single snowflake falling on Christmas Day.
“In terms of a white Christmas, it looks likely, with wintry showers possible over high ground in the far north of Scotland, but not widespread,” said Met Office spokesman Stephen Dixon.