The “remnants” of the storm that brought severe blizzards to the US is hitting parts of the UK, bringing heavy rain, gales and travel problems.
Western areas are bearing the brunt, including Cumbria, where some schools have closed and roads are flooded.
Ferries to the Scottish Islands and Isle of Wight are disrupted, and in Edinburgh, a man was hurt when a broken chimney smashed through a bus window.
The Army is working to help shore up defences in some high-risk communities.
The Met Office has issued yellow – be aware – warnings for rain and there are more than 90 flood warnings and alerts in place.
BBC Weather’s Darren Bett said although the wet and windy conditions were affecting many parts of the UK, the wettest weather would be in the west in Cumbria, the Welsh hills and the moors of the south west.
He said dry afternoons were forecast on Tuesday for Scotland and Northern Ireland, following heavy rain this morning.
Some 20-40mm (0.8-1.6in) of rain – and up to 60mm in the most exposed areas – is forecast in Scotland, while north-west England, Wales, Devon and Cornwall are predicted to get between 30 and 50mm, with up to 100mm in exposed uplands.
The storm in the US brought near-record snowfall from Washington to New York.
Its arrival in the UK was expected to bring bad weather in two main waves – one late morning and afternoon on Tuesday, and another Tuesday night into Wednesday.
There is also a warning in place for heavy rain for Northern Ireland on Wednesday, when gale-force winds are expected.
The Environment Agency said it was monitoring river levels. There are currently nine flood warnings, meaning flooding is expected: five are in Cumbria, three in Dorset and one in the Conwy Valley.
There are also more than 80 flood alerts – meaning flooding is possible – in England and Wales.
The agency said rivers in Cumbria, Lancashire and Yorkshire were already at record levels following the wettest ever December.
There was also a possibility of “some flooding” along the rivers Severn and Wye.
The Scottish Environment Protection Agency (Sepa) currently has nearly 50 flood warnings and nine flood alerts in place.
Environment Secretary Ms Truss chaired a meeting of the government’s emergency Cobra committee on Monday in preparation for the bad weather.
She said “all possible steps” were being taken to prepare for the storm.
Clare Dinnis, the Environment Agency’s national flood duty manager, also urged people to take care near coastal paths and promenades, and not to drive through flood-water.
More heavy rain is forecast for Friday, with warnings already in place for parts of Scotland, Northern Ireland, north-east England and Wales.