A tropical plume will cleave the jet stream into fragments ushering warm gusts from Africa to finally unlock summer. Temperatures next week are widely tipped to rocket into the high-20Cs or even the low-30Cs. A U-turn in weather patterns will shunt low pressure to the north allowing southerly high pressure to build across the UK. Britons will grit their teeth through just a couple more days of gloom before Sunday douses the nation in sunshine. Met Office meteorologist Annie Shuttleworth said: “As we head towards the weekend, the jet-stream shape slowly starts to change, buckling more and devel…