Temperatures could hit 20C in parts of the UK on Wednesday, while flooding is possible amid yellow weather warnings for heavy rain, the Met Office said.
Heavy rain across parts of Wales and west England prompted the Met Office to extend its warning for parts of south-west England, the north and east Midlands, north-west England and Wales until 9pm on Wednesday, where some areas could see 50 to 80mm of rain in six hours.
Another yellow warning has been issued from midday Wednesday to midnight and includes north-east and north-west England and Yorkshire and Humber.
Many areas will see 20mm of rain but some could have 50 to 80mm in six hours, and isolated thunderstorms are possible, the Met Office said.
Mild temperatures are forecast, with highs of 20C or 21C in the south – about 5C warmer than the average for this time of year – while 13-18C is forecast for most, the forecaster added.
Met Office meteorologist Greg Dewhurst warned on Wednesday morning that spells of heavy rain could lead to travel disruption and flooding in places.
Mr Dewhurst said: “Outbreaks of rain have been pushing north across the night.
“The rain is quite extensive across parts of Scotland, Northern Ireland, Wales and the west of England, and when it’s not raining it’s cloudy, misty and murky.
“It will stay pretty similar in terms of the areas that will see the outbreaks of rain, it could be heavy at times.
“The driest will likely be across the east and south-east of England.
“It will start to become drier across the south-western parts overnight; by the end of the night it will be more restricted to parts of Scotland and north-east England.
“Tomorrow there will be rain first thing across Scotland and north-east England. It will quickly clear and be a much brighter day for everyone. There will be a few showers but lots of places will stay dry and temperatures will be between 16-19C.”
The forecaster added that on Friday there will be a west and east split developing with cloud and rain in western parts of the UK while central and eastern areas will be dry with sunny spells. Temperatures will be between 13-16C.
The warning comes after heavy rainfall caused widespread flooding across the UK in September and early October.
Some counties of England saw their wettest September on record, receiving three times the normal rainfall, and Oxfordshire and Bedfordshire had their wettest months ever – although the rain came after a drier than normal summer for much of the UK.