Heavy rain is expected across Northamptonshire and the south of England on Thursday with potential localised flooding, before spreading north during the day.
The yellow weather warning is active from 1am tomorrow (Thursday) through until 11.50pm, and the rain is likely to be accompanied by thunder and lightning, with potential torrential downpours.
The Met Office are warning the public to be aware of a significant risk of very localised disruption to travel due to surface water flooding.
Senior MeteoGroup forecaster Julian Mayes added: “A thundery area of low pressure is developing over northern Spain and this will spread warm, humid air northwards over the next two days.”
15 to 30 mm of rain is possible in in 6 to 12 hours, with as much as 50 mm possible very locally by the end of Thursday.
A further Met Office warning is in place for the whole of Friday, as the area of heavy rain is expected to push across the rest of England during the morning.
The rain is likely to be persistent, and accompanied by hail and thunder in the south and east.
Localised thunderstorms may develop across the south and east of England during Friday afternoon, these potentially giving 15-25 mm of rain in a few hours.
Rain will ease from the west during the evening, probably confined to eastern areas by the end of Friday, with drier, fresher weather following on Saturday, with some sunshine.
The AA is warning drivers to be careful.
Paul Watters, head of roads policy, said: “Flash-flooding in the summer can be hit-and-miss but potentially dangerous for anyone caught up in it. The AA advises drivers to keep an ear out for local weather warnings and traffic news, and be prepared to encounter flooding.
“Flooding close to where you live may present less of a problem as most drivers know which are the hazardous stretches of road and can avoid them. Those on holiday face a more precarious challenge and asking local people where they might run into flooding is a wise move.”
The AA warns motorists only to drive through water if they know it is not too deep - generally this would mean no more than halfway up the wheels. Also they should not try driving through fast-moving water, such as in a ford - the car could easily be swept away.
A spokesman said: “If you are driving and become stuck in flood water, it’s generally best to stay in the car and telephone for help rather than try to get out - unless the water is shallow, stationary and you can see the ground beneath the water.
“If you return to find your car standing in flood water it’s best to leave it and telephone for help or wait for the flood water to subside, rather than try to get to it and move it - unless the water is shallow, stationary and you can see the ground beneath the water.”