The Met Office say it is expected the storm, with wind speeds of 80mph or more, will cross the southern half of Britain, rather than passing south of the country, but will not come further north than the border.
The Met Office issued an amber warning, meaning "be prepared", for the southern half of England and the southern half of Wales.
It gave a lesser yellow warning, meaning "be aware", for the rest of Wales and England up to the border with Scotland.
The storm, likely to be the worst of the year so far, will develop over the Atlantic tomorrow before bringing exceptionally strong winds to land early Monday.
Met Office spokeswoman Nicola Maxey said: "We have been tracking the probable course of the storm, and we are tracking it further north than we had thought earlier. We have also revised the speed for gusts of wind up to 70 to 80mph inland, with the possibility of speeds in excess of 80mph in exposed coastal areas."
She said there was the possibility of structural damage, trees and power cables coming down, and transport problems.
"We are expecting the storm to be in the early hours, and it is not yet clear how long it will take to cross the country. The rush hour will see the aftermath, with any damage, power and transport problems that have occurred."