Warnings of disruption from thunderstorms have been issued for the northern parts of the UK while southern England can expect what may be the hottest day of the year so far. Temperatures were expected to reach 34C or more in the south-east on Monday. So far the hottest day of the year in the UK was recorded on 19 July when a temperature of 31.9C was recorded at St James’s Park in central London. A spokesperson for the UK Health Security Agency confirmed a yellow heat health alert is in place until Tuesday 9am in England for London, the south-west, south-east, east of England, East Midlands and West Midlands. A kink in the jet stream, caused by Storm Debby in the US, is pushing hot air northward and is expected to cause storms. The Met Office has issued yellow warning for thunderstorms on Monday for northern England, Scotland and Northern Ireland. It warns that “sudden flooding” could lead to difficult driving conditions and some road closures. And there is a small chance that some communities could become temporarily cut off by flooded roads. The Met Office also said there is a slight chance of power cuts to homes and businesses as some gusts could hit gale force with the strongest winds in northern Scotland. The warning said: “Although not all parts of the warning area are expected to see them, an area of increasingly organised thunderstorms is likely to produce a combination of frequent lightning, heavy rain, hail and short periods of strong winds. Some torrential downpours are likely, with 20-40mm in places, and a potential for 40-60mm of rain to fall in one to two hours very locally, with hail up to 2cm in diameter.” It added: “Prepare to protect your property and people from injury. Before gusty winds arrive, check to ensure movable objects or temporary structures are well secured. Items include: bins, garden furniture, trampolines, tents, gazebos, sheds and fences.” The thunderstorms are forecast to clear towards the north-east by Monday afternoon. The hot temperatures in the south are expected to return to more normal levels for the time of year by midweek. The high temperatures will bring a rise in pollen count from nettle and mugwort pollen and high UV levels. The Met Office recommends covering up during midday hours and wearing sunscreen.