Britain will experience a split in weather conditions tomorrow with heavy downpours set to hit the West while eastern areas enjoy unseasonable highs of up to 22C.

The Met Office imposed a rain warning for western England from Manchester down to Plymouth and much of Wales, running from 6pm tonight until 12pm tomorrow.

More than three inches (80mm) could fall within six hours along with thunderstorms and lightning, bringing a risk of communities becoming cut off by flooded roads.

But conditions are also turning much milder with southerly winds transporting a warm and humid airmass from the western Mediterranean and North West Africa.

Temperatures hit 18C (64F) in London this afternoon before parts of the South East could reach 22C (72F) tomorrow, with the mid to high teens expected in other areas.

Met Office chief meteorologist Matthew Lehnert said: ‘Warm air arriving from the south will allow temperatures to rise above average despite it often being cloudy.

‘On Wednesday, parts of South East England could see 20C (68F) or 21C (70F), with the mid to high teens expected across many parts of the UK. However, this warm and humid airmass will bring with it a risk of heavy rain and isolated thunderstorms.’

Later this week, forecasters expect further bands of rain moving across the UK, and while temperatures will fall slightly it will remain mild for the time of year.

Met Office deputy chief meteorologist Dan Holley said: ‘A low pressure system could bring strong winds to the North and West on Friday.

‘This combined with high spring tides may result in some coastal impacts, potentially continuing into the weekend on some coasts.

‘As we head into the weekend the weather will remain unsettled with further rain at times, and by Sunday there is a chance that a particularly deep area of low pressure arriving from the Atlantic could bring more widespread strong winds, especially in northern and western areas, with potential for some disruption in places.

‘This low pressure system is not expected to develop until Friday near the coast of Canada, so at this stage there is still a lot of uncertainty about the strength and track of this system as it interacts with the jet stream over the weekend.

‘We’ll keep reviewing the need for any warnings over the coming days, so it’s important to stay up to date with the latest forecast.’

Zoe Hutin, a meteorologist at the Met Office, also said: ‘The main regions that will be affected (by the first warning) are central Wales, South Wales, parts of the South West of England and pushing as far north as Cheshire and Manchester.

‘It will be from Manchester all the way down to Plymouth. Everywhere in that region is likely to see 10 to 12mm, but there are a few places that could see considerably more, potentially up to 80mm of rain in six hours.

‘At the moment it’s difficult to say exactly where. The most prone spots will be the most central areas of the warning but it could be anywhere within that region. Those most prone to flooding will also be affected, particularly if they are low-lying.’

The warnings come 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.

Oxfordshire and Bedfordshire had their wettest months ever – although the rain came after summer, which was drier than usual, for much of the UK.

Ms Hutin said: ‘The land has had a chance to dry so it’s not like we’re holding on to excess flood water from previous rain events. 

‘But given some areas have already had a fair amount of rain in the past six weeks and it’s been a particularly wet season so far, particularly in central England, this rainfall is not going to help with any bodies of water that are higher than usual for this time of year.’

In Northern Ireland, the rural areas of the south east are expected to see the most rainfall.

Ms Hutin said: ‘There’s not a huge population in this part of Northern Ireland so it’s not going to be too impactful to a huge proportion of people.

‘But it is a bit of land that is particularly susceptible to flooding, so while the rainfall may not be particularly (large) – we’re generally expecting 20 to 30mm – the area is quite low and reasonably marshy which means this amount of rain will have a greater impact on this region.

‘But some high grounds could see up to 50 or 80mm which is fairly high for a six to 12-hour window.’