Three days of bad weather are set to lash the UK, with as much as three inches of rain predicted to fall in some areas.
As the washout end to July continues the Met Office issued yellow weather warnings for much of Wales and northern England, and an amber weather warning for Scotland.
But while heavy showers will continue throughout the week, meteorologists said sunny spells will break through the gloom.
Met Office chief meteorologist Steve Willington said: "Yellow warnings are in place across much of the UK, away from the south, for thunderstorms and heavy rain over the coming days.
"Scotland, however, is expected to see some of the heaviest rain and amber warnings for thunderstorms and also rain have been issued here."
Meanwhile, 15 flood alerts have been announced by the Scottish Environment Protection Agency, for areas including Aberdeenshire, Dundee and Angus, Fife and West Central Scotland.
Stephen Dixon, a spokesperson from the Met Office, said there was an amber weather warning in place from 6am on Wednesday to 6am on Thursday in Inverness.
He said: "The rain can cause potential flooding and travel disruption.
"There is the potential for 80-100mm over 24 hours, but more likely 60mm more widely across that amber area.
"There can possibly be lightning and hail in areas of Scotland."
In England and Wales, 20-30mm of rain is possible up to Wednesday, the Met Office said.
Mr Willington added: "Not everywhere within the warning areas will see heavy rain, rainfall amounts will vary from place to place.
"The rainfall could lead to some surface water flooding and disruption before it eases and moves south through Thursday."
Over the past few weeks, rain has battered the UK, particularly in London where areas including Walthamstow, Woodford and Stepney Green have seen flooding.
London Mayor Sadiq Khan announced on Tuesday that following a meeting with the Environment Agency, London's boroughs and other key partners, he will be doing all that he can to tackle flooding and climate change.
He said: "Through the new London Plan, we're now reducing the risk of surface water flooding with every new development, but whether it's prioritising more green spaces to help absorb excess water or investing more in upgrading our drainage and sewer infrastructure, dealing with the impacts of climate change is something that cannot wait a day longer."
UK five-day weather forecast
Today:
Rain will be heavy and prolonged at times across central and northern Scotland with a risk of thunder. Elsewhere, scattered showers along with sunny spells, some of the showers being heavy with thunderstorms in places by afternoon. Breezy.
Tonight:
Rain at times across Scotland easing, but further heavy showers across central UK, particularly affecting northwest England. Southern areas, breezy and becoming mostly dry with clear spells.
Thursday:
Drier across southern areas than recent days with sunny spells. Cloud and rain over Scotland moving south into Northern Ireland and northern England, but turning more showery.
Outlook for Friday to Sunday:
Showers for many Friday, prolonged across southern areas during the morning. Showers become confined to southern areas over the weekend, with a lot of dry weather elsewhere. Generally rather cool.
