A FREAK mini heatwave will send thermometers rocketing to 32C (90F) on Saturday before tropical storms hit Britain.
Swathes of the country will swelter in a “Spanish plume” from the Continent with summer to a close on a monsoon deluge.
Torrential rain, gales and ferocious thunderstorms triggered by volatile Atlantic weather systems threaten a chaotic end to August.
Despite the steamy outlook over the coming days forecasters warn to batten down the hatches in the run up to the bank holiday.
The mercury will soar into the high 20Cs across the south tomorrow (Saturday) with a slightly cooler 21C (70F) elsewhere.
Torrential downpours will dump more than two inches of rain across central regions from the afternnon sparking fears of sudden and disruptive flash floods.
Forecasters have blamed the frenzied weather picture on a powerful jet stream dragging storms in from the Atlantic.
Leon Brown, forecaster for The Weather Channel UK, said the rest of the month looks unsettled with a glimmer of sunshine hope for the bank holiday.
He said: “Saturday may well be hot and humid over eastern England with temperatures in the higher 20s, possibly 28C in the southeast.
“Heavy downpours are developing though across central Britain with a risk of flash flooding from storms, but also wide areas at flood risk with 40 to 60mm [2.4ins] falling between Saturday and Sunday afternoon.
“Through next week several more depressions are likely to run across western and northern Britain in the jet stream with a further risk of strong winds and some heavy rain.
“As we head towards the holiday weekend it now looks like the UK will still be under the jet stream so we can expect more unsettled weather.”
Britain’s bonkers weather over the past few weeks has baffled forecasters who have struggled to settle on a definitive outlook.
They blame the unusually wavy jet stream and a series of low pressure systems for throwing forecasts out of kilter.
Although they now agree on an unsettled and muggy run up to the end of summer, the outlook could still change.
Chris Burton, forecaster for The Weather Network, said Britain is about to become a “battleground” between Continental and Atlantic air masses.
He warned Wales, south-west England, northern England and southern Scotland to brace for the heaviest downpours in the coming days.
He said: “A battle between hot and humid air from the continent and cooler, fresher air off the Atlantic will take place over the UK this weekend bringing the risk of torrential downpours.
“South-easterly winds will develop across eastern areas of England into Saturday, drawing in some very hot and humid air from France.
“Temperatures will widely soar into the mid to high 20Cs across south-east England, East Anglia and the East Midlands with some spots likely to hit 30C.
“Where the hot, humid air and cooler, fresher air clash, heavy and potentially thundery downpours are likely to develop overnight into Sunday.
“Heavy rain will continue across western areas during Sunday, but it may well remain hot and sunny across the eastern half of England for much of the day before the wetter and fresher conditions spread in.
“Next week looks like remaining unsettled, but with the fresher conditions spreading across all parts of the UK as winds blow in from the west or south-west.”
James Madden, forecaster for Exacta Weather, said: “There has been a contrast among forecasters and various model indications of late.
“There has been a battleground scenario between high pressure settling things down and strengthening weather systems pushing in from the Atlantic, which leaves us with nothing entirely settled.
“Throughout the weekend Sunday and into Monday low pressure will push near to the UK and this could bring a more unsettled, wetter and somewhat potentially windier outlook.
“However, it will feel warm and muggy for many prior to this particularly in some southern and eastern parts of the country where temperatures could approach the mid to high 20s in places on Saturday.
“We may also see some thunderstorms being triggered off in some western parts on Saturday and in some southern areas throughout the weekend and into early next week as we retain the muggy and warmer weather.”
The Met Office said after a mostly chilly week temperatures will start to rise on Friday with highs of 25C (77F) likely in parts.
Warm air from France will however trigger storms with Britain on alert for thunder, hail and torrential downpours at the weekend.
Spokeswoman Laura Young said: “We are now confident that it is going to be unsettled with very heavy showers likely from Sunday.
“Saturday is looking very warm in parts in in those places it won;t be a bad day, however under cloud cover it will be much cooler.
“The heaviest rain will set in during the evening from Wales and the southwest and it is remaining unsettled into next week.”
Netweather said ground temperatures in isolated spots in the south could hit a steamy 32C on Saturday before things turn cooler.
MeteoGroup said a “Spanish plume” would send temperatures rocketing towards 32C (90F) by the weekend,
Forecaster Julian Mayes warned a surge of heat from the Continent will trigger “severe thunderstorms” from Saturday.
He said: “As the wind becomes southerly on Friday and Saturday, a brief surge of heat from the Continent will affect central and eastern parts of England. However, heavy rain is likely to become widespread through the weekend, especially in the west and north. Severe thunderstorms may affect some areas.
“A subtle difference in wind direction promises at least one day of fairly hot weather for parts of the country.
“The areas most likely to see this are central and eastern England, as hot air from the Continent pushes northwards as a weather pattern termed colloquially by meteorologists as a ‘Spanish Plume’ develops.
“Saturday looks to be the hottest day, and temperatures may reach around 30°C in London, 28°C in Norwich and Cambridge, and 25 or 26°C in Bath, Birmingham, and Lincoln.”