Temperatures in the Sahara are expected to peak in the next 48 hours as government heat warnings give way to thunderstorm warnings.
Dramatic downpours caused by storms, hail and lightning strikes threaten travel chaos, power outages and “risks” from a nationwide electrical outburst.
Weather models show that relative humidity – the measure of humidity in the air – shoots up to 100 percent over parts of Britain.
The Met Office issued a series of thunderstorm warnings starting Monday for up to two inches of rain, which could lead to flash flooding and damage to buildings.
Jim Dale, meteorologist for British Weather Services, said: “The downpours will be quite large with the potential for severe widespread thunderstorms.
“While temperatures are starting to drop this week, Monday still has the potential to get very warm in the south of Britain. Very high temperatures with heavy rain early next week will increase the humidity.”
But torrential rains on bone-dry ground will cause flash flooding instead of alleviating the drought crisis. The National Drought Group, a collective of government officials and water companies, has added eight areas in England to its list.
Devon, Kent, Lincolnshire and East Anglia are officially in drought with bans on the use of garden hoses lurking next week.
Mr Dale, author of Weather or Not? and a severe weather expert said: “There will be torrential rains at the beginning of the week, but these will not help the situation.
“The only thing that will replenish water supplies is prolonged and constant rainfall. Heavy rain as we expect will only drain off the ground and cause flooding problems.”
Driving rain will be driven in part by the jet stream as it flows over the UK and over Great Britain. It will sink south today to collide with a low-pressure system near the UK, according to the Met Office.
Meteorologist Aidan McGivern said: “The jet stream is evolving from North America, and the wind is getting stronger and pushing over the Atlantic. The dip in the jet stream by Sunday will pick up a low pressure area.
“For most, Sunday will be another sunny and very hot day, and there is a chance of some showers or thunderstorms further north over higher parts of Scotland and northern England, but these showers will be isolated.
“By Monday the jet stream will dive south and combined with low pressure increasingly hitting the UK we are likely to see an increased risk of showers and thunderstorms.”
With temperatures still in the 30Cs, parts of Britain will have to wait until later in the week to cool down, he warned. He said: “Tempers will reach 30C and above, and through Monday showers will develop more widely, and there will be a risk of thunder and lightning. The temperatures are going to drop.”
Thermometers will skyrocket again today, with peaks expected in the mid-30s, especially in the south. Scotland and Northern England will be fresher with winds and showers keeping the mercury between 22C and 30C.
In Wales and Northern Ireland, thermometers will fluctuate between 25C and 30C, while central and southern England bear the brunt of the blowtorch attack. South Britain will hold the heat as the rest of the country begins to cool, forecasters predict.
James Madden of Exacta Weather said: “The more noticeable change will initially be in parts of the north in terms of cooler temperatures and frequent showers.
“There will be a noticeable drop in temperature in the south then, but it will still feel warm for the time of year because the heat continues here.”