The Scottish Environment Protection Agency (Sepa) issued 13 flood warnings within Tayside alone yesterday, to last until about noon today, while general flood alerts were announced for west central Scotland, Central, Borders, Dundee and Angus, Dumfries and Galloway, Aberdeenshire and Aberdeen City.
As the agency also warned of more flood problems for tomorrow, the Scottish Government said its Resilience Room had been in operation since before Christmas and was ready to deal with any further problems.
The downpour meant the Scottish rugby derby in the Pro12 between Glasgow Warriors and Edinburgh was postponed after a 5pm pitch inspection at Scotstoun Stadium.
With rain falling heavily for several hours before the scheduled 6pm start, the match was called off within an hour of kick-off because the pitch was waterlogged.
Edinburgh captain Greig Laidlaw said: "It is extremely disappointing for everyone, but the pitch is in a pretty bad state and even to get drop-outs 10 yards was going to be difficult."
The Met Office said any rain hitting Scotland would hang around the east coast until dawn today.
Flood warnings for Tayside say that with high loch levels and saturated ground conditions, river levels will become high again into today. The agency warned that low lying agricultural land was at risk of flooding.
But a Sepa spokesman warned of further mayhem elsewhere tomorrow, saying a storm surge coinciding with high astronomical tides may bring the risk of coastal flooding.
Flood alerts, which mean flooding is possible tomorrow, are likely be issued for Ayrshire, the Clyde estuary, and Loch Linnhe. But more areas could be affected.