Drivers are being warned to take extra care as torrential downpours are forecast for Monday afternoon and into the evening rush-hour.
The Met Office has upgraded its existing yellow (Be Aware) alert to amber (Be Prepared) in parts of Angus, Perth & Kinross, Fife, Central, Strathclyde, North and South Lanarkshire as well as the Lothians and the Borders, including Dundee, Perth and Edinburgh.
The area is likely to see some heavy downpours with the possibility of large hailstones and significant disruption from surface water flooding, especially in urban areas.
There could be as much as 20mm to 30mm of rain falling in two hours, with 50mm to 60mm expected over the course of the afternoon.
Surrounding the core amber area there will be a yellow warning covering most of the eastern side of Scotland, from South Aberdeenshire down to the Border and going as far west as west Glasgow, east Ayrshire and the east of Dumfries and Galloway.
Transport minister Keith Brown said: “The Met Office is warning us that there could be some significant disruption in parts of Angus, Perth & Kinross, Fife, Central region, Strathclyde, North and South Lanarkshire as well as the Lothians and the Borders from extremely heavy showers later today.
“The rain will have an impact on some areas, including Dundee, Perth and Edinburgh during the evening rush-hour, and motorists should drive according to the conditions by allowing extra time for braking and be aware of surface water.
“Transport Scotland officials are in regular contact with the Met Office and other key responders to ensure that suitable preparations are in place and that ministers are receiving regular updates.
“Our multi agency response team remains on stand-by and our operating companies are closely monitoring the situation, and are ready to deal with any weather-related issues that arise.
“The travelling public also have a key role to play. The Traffic Scotland website, variable message signs and traffic internet radio are being used to provide up-to-date information, allowing them to plan and amend their journeys accordingly.”
Nigel Goody, hydrology duty manager for the Scottish Environment Protection Agency (Sepa), said: “With a predicted period of heavy thundery showers, and a possibility of heavy hail, this afternoon, there is a risk of significant surface water flooding anywhere across Central, Tayside, Dundee and Angus, Fife, Edinburgh and Lothians and the Scottish Borders.
“This is expected to result in localised travel disruption at known trouble spots as showers develop throughout the afternoon.
“Particular areas of concern are populated centres around Dundee, East Tayside, Fife and the eastern parts of the Central belt. Some smaller watercourses may experience minor flooding impacts, but main rivers are expected to cope with this afternoon’s rainfall. The flood risk will ease as the weather recedes into this evening.
“Sepa will continue to monitor the situation and would encourage members of the public to check the Sepa website for active flood alerts or call Sepa’s Floodline on 0845 988 1188, for the most up-to-date information on their area.”