More than a month's rain is expected to fall over just two days in parts of the UK this week.
A severe weather warning has been issued by the Met Office, with fears of flooding and disruption on Friday and Saturday.
Central and northern England is expected to be worst affected, with an amber alert - the second most severe category that can be given - in place for north-east England.
Up to 100mm (3.9 inches) of rain could fall in 36 hours during the downpours
The average UK rainfall for July is 69.9mm (2.8 inches)
64.4mm (2.5 inches) for the north of England
People living in the affected areas have been warned to be prepared for flooding.
Less severe yellow warnings have been issued for much of England and Wales and parts of southern Scotland for Friday.
The deluge could affect the men's semi-finals at Wimbledon which are scheduled to take place on Friday.
While Friday's downpours will be the most widespread, the Met Office has also issued yellow weather warnings for some areas of the UK for today and tomorrow. The heaviest rain today is expected in the north-east and central areas of England, with some storms predicted in south-west England tomorrow.
Last month was the wettest June since records began, with double the average rain falling during the month. Provisional figures from the Met Office showed:
the UK received 145.3mm (5.7 inches) during June
that beat the previous record of 136.2mm (5.4 inches) in June 2007
It was the second month this year to see record-breaking amounts of rain
April became the wettest in the records dating back more than a century to 1910
June saw long, prolonged rainfall and short but exceptionally heavy showers, ending with freak storms battering areas of the Midlands and the North East.
The exceptional amount of rain caused floods in Wales and parts of England.