Thunderstorms and flash floods forecast in some areas; 30mm of rain could fall in an hour

This article is more than 2 years old

This article is more than 2 years old

Friday could be the UK’s hottest day on record, forecasters have warned, adding that Thursday was unlikely to be much cooler, as the extended heatwave that has hit the country continues.

The Met Office predicted temperatures in the south-east of England as high as 37C on Friday – in places potentially even surpassing the previous all-time high of 38.5C – and only a couple of degrees cooler on Thursday.

The lengthy hot and dry spell, which has particularly affected eastern England, is likely to be broken by thunderstorms towards the end of the week that could bring rainfall of as much as 30mm (1.18in) in an hour, forecasters said.

While many have enjoyed the weather, there were warnings on Wednesday to avoid “careless and reckless” behaviour as emergency services across the country deal with grass fires in the aftermath of the major incident on moorland to the east of Manchester. The NHS said demand for online health advice through its NHS Choices service in July had increased 450% year-on-year.

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“The heatwave conditions will continue across much of England, with temperatures into the mid to high 30s Celsius in many places from the Midlands eastwards on Thursday and Friday and it’s possible that we could break the all-time UK record of 38.5C if conditions all come together,” said the Met Office’s chief meteorologist, Paul Gundersen.

Quick guide Your forecast from the Met Office Show Hide Eastern England A dry and muggy night is forecast on Wednesday, with some mist and fog north of the Wash. Thursday is expected to be hot, with temperatures reaching as high as 35C in southerly areas and 26C in the north. Thunderstorms could develop all over eastern England later in the day. Friday and the weekend are likely to remain hot, if a little cooler, and there will be the continued risk of thunderstorms on Friday and further rainfall during the weekend. Western England A dry night is expected on Wednesday, with temperatures not falling below 14C in southerly areas, and 11C in northerly. It is forecast to be hot throughout on Thursday, with maximum temperatures between 31 and 32C, though thunderstorms could hit the Pennines and there could be some hazy weather to the south. Friday and the weekend will likely still be sunny, though it could be a little cooler and with the risk of rain persisting. Wales Wednesday night is likely to be dry and warm, with temperatures not falling below 10C. Thursday is forecast to be sunny and hottest in easterly areas, where temperatures could get as high as 30C. Westerly areas are still likely to be warm, but should see light winds. Friday and the weekend are not expected be as hot and there is a risk of showers, turning into persistent rain on Sunday. Scotland A largely fine evening on Wednesday, though the weather could turn a little chilly in rural areas. Thursday is likely to be very warm, with temperatures in the mid-20s throughout Scotland – barring Orkney and Shetland. The weekend is likely to bring rain throughout the country as it wears on. Northern Ireland Slightly cooler than most of the rest of the country on Wednesday night, with a minimum temperature of 9C and some cloud to the west. Thursday will be dry and sunny, especially in the east, while that westerly cloud could bring rain. The maximum temperature is predicted to be 25C. Friday and the weekend are likely to see outbreaks of showery rain, interspersed with some cloudy and some sunny weather.

“There is the chance of thunderstorms breaking out over some eastern parts of England on Thursday, but it is Friday when we see intense thunderstorms affecting many central and eastern areas,” Gundersen added.

“While many places will remain dry and hot, the thunderstorms on Friday could lead to torrential downpours in places with as much as 30mm of rainfall in an hour and 60mm [2.36in] in three hours. Large hail and strong, gusty winds are also likely and combined could lead to difficult driving conditions as a result of spray and sudden flooding.”

The Met Office issued a yellow warning of thunderstorms, its second most severe, covering the whole of eastern England from the Scottish border to Bedfordshire, excepting East Anglia and the southern part of the Wash from 2pm to the end of Friday.

The highest temperature on record in the UK is 38.5C, which was observed at Faversham in August 2003. This year’s hottest day so far was Monday, when Santon Downham in Suffolk saw temperatures of 33.3C – a little more than a degree less than 2017’s highest.

Fears that tracks will buckle led to speed restrictions on Chiltern Railways, Greater Anglia and Northern lines on Wednesday. Cutting the speed of trains reduces the force they exert on the track.

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A spokeswoman for Network Rail said: “On very sunny days, rails in direct sunshine can be as much as 20C above air temperature, causing the steel to expand markedly.

“Our engineers and specialist extreme weather teams are monitoring trackside temperatures and vulnerable locations and will, if necessary, introduce temporary speed restrictions during the hottest part of the day to keep trains running, albeit more slowly than normal.”

Many journeys on the UK’s motorway network were also taking as much as half an hour longer.

“Summer is always a busy time for breakdowns and we tend to see a lot of tyre problems, overheating engines and keys locked in cars,” an AA spokesperson said.

In London, the mayor, Sadiq Khan, issued a “high air pollution alert” for Thursday, as rising temperatures combine with pollution from the continent to create dangerous conditions.

Adults and children with lung problems, as well as adults with heart problems, were advised to reduce their physical activity.

Last week, the Guardian reported a spike in asthma deaths due in part to the pollution crisis and doctors have said anyone with the condition may need to use their inhalers more often.