Yellow warnings of rain have been issued for Lancashire for Monday, Tuesday and Wednesday.
Met Office experts issued a warning for the county on Monday, to last until 9pm.
Forecasters said scattered heavy thundery showers were expected to develop, and warned of possible localised flooding and travel disruption.
A statement said: “Low cloud will slowly break allowing temperatures to rise, triggering some heavy and slow-moving downpours.
“15-25mm could fall within an hour in scattered locations, bringing the risk of flooding, especially if across urban areas.”
Another warning has been issued for Tuesday, from 10am to 9pm.
A message on the Met Office website said: “Scattered heavy, thundery showers are expected to develop again on Tuesday, and will lead to slow-moving downpours across the warning area.
“Many locations will miss these, but where they do occur, please be aware of possible localised flooding and disruption to travel.”
And more warnings are in place for Wednesday, from 10am to 9pm, with similar conditions expected.
Flash flooding struck the county on Monday, with cars submerged in deep water on roads in Lancaster and fire crews called out.
A number of roads were partly closed after heavy rain hit Lancaster and Morecambe on Monday morning.
In the early hours of Monday, fire crews were called to flooding in a flat in Curwen Street.
A blocked drain and heavy rain had resulted in water coming through the ceiling of a first-floor flat.
Firefighters from Preston pitched a ladder to access the drain and clear it.