Portsmouth weather could reach 36C and beat record held by Southampton amid heat warning

An extreme heat warning has been expanded as the UK braces for a sweltering heatwave that could see record-breaking highs.

The Met Office said the blistering heat could last until at least Thursday, sparking weather warnings, health alerts and concerns for vulnerable people.

Forecasters have said there is “growing confidence” this week could break the record for the hottest June temperature of 35.6C, which was set in 1976 in Southampton. Portsmouth is forecast to hit 36C on Thursday which would break the record.

On Monday, Portsmouth is expected to see a high of 31C, on Tuesday 32C and Wednesday is expected to hit 34C.

A Red warning for “extreme heat” has now been issued by the Met Office covering parts of Hampshire. “An exceptional spell of hot and humid weather is expected across this region, with impacts to the general population highly likely,” the forecaster said.

The coming days will see humid conditions and potentially tropical nights, when the overnight temperature does not fall below 20C, making it feel “muggier” than last month’s heatwave, the Met Office said.

The UK Health Security Agency (UKHSA) warned people to expect significant impacts across health and social care services along with a rise in deaths, particularly among those aged 65 and over or with health conditions.

On Sunday, an amber extreme heat warning issued by the weather service was expanded to last from Monday until Thursday.

The alert flags potential health impacts for people vulnerable to extreme heat and heat-related issues for the wider population, as well as a possible increase in water safety incidents. Monday and Tuesday’s warning covers most of southern England.

People in the alert area are advised to drink plenty of fluids and keep out of the sun, and avoid exercising between 11am and 3pm, the Met Office said.

Substantial changes to working and daily routines will likely be required and disruptions to road, air and rail travel should be expected, according to the weather service.

Met Office meteorologist Simon Partridge said: “It’s a very unusual, very rare spell of very hot weather, so it’s one of those ones where people should take care, try to keep their houses as cool as possible, check in on those that are vulnerable, so the very young and very old, in particular, are more vulnerable to extreme heat.

“But everybody will feel this because it will be very hot and the overnight temperatures, in particular, will mean that people won’t be getting as much sleep, probably, as they would usually do, so it will affect everyone.

“There’s also potential for impacts to transport as well. We know that when things get very warm, there can sometimes be issues with railway lines, and even possibility that some roads might not be doing too well.

“If it gets too warm, you may even see a little bit of tarmac melting at times.”