Red warning: the UK's first 40°C June is on the table — and so is the breakdown

The Met Office has issued a red Extreme Heat warning — its highest level of alert — for central and southern England, and Wales, running from 0900 Wednesday to 2100 Thursday (24–25 June). A red warning is rare, and it carries a blunt message: this is a risk to life for everyone, not only those usually considered vulnerable.

Temperatures are forecast to reach at least 39°C, and potentially higher, with the south already climbing to 37°C on Tuesday and southeast Wales to 35°C. The UK's June temperature record of 35.6°C (set in 1976, equalled 1957) is very likely to be broken, and Wales' June record of 33.7°C looks set to fall too. 40°C in June — never recorded in the UK — is on the table.

Why this one is different

The danger isn't just the daytime peak. The Met Office is forecasting widespread tropical nights, with temperatures staying above 20°C overnight — especially in towns and cities — and dew points around 22°C making the air oppressively humid.

"Consecutive nights where temperatures do not drop below 20°C will make it very hard for people to recover from the daytime heat, exacerbating heat stress impacts." — Mark Sidaway, Met Office Deputy Chief Forecaster

No overnight relief means the heat load compounds day on day. That is what turns a hot spell into a health emergency.

The implications

• Health — heat-related illness across the whole population, not just the elderly or unwell. Stay out of the sun 11am–3pm, hydrate, and never leave anyone or a pet in a parked car.
• Infrastructure — buckled rails, speed restrictions and cancellations; roads softening; significant travel disruption likely.
• Power and water — surging demand for cooling and water stresses the grid and supply network; localised outages possible.
• Water safety — the rush to cool off drives drownings. Cold-water shock is real even in a heatwave — the RNLI advises lifeguarded beaches only and Float to Live if you get into trouble.
• Wildfire — baked vegetation and tinder-dry ground raise the fire risk sharply, particularly on heath, moor and grassland.

The chase read

For chasers, the heat is the prologue. The breakdown is the story. Every hot, humid afternoon banks energy:

• Instability is the headline. CAPE climbs through the warning period — check the outlook for where the cap is weakest when the trigger arrives.
• Shear is the question mark. Flow stays light under the ridge; watch the wind atlas for deeper shear nosing in from the west — that's when pulse storms start to organise.
• Timing beats positioning. Like every UK breakdown, the window is late afternoon into evening and it moves fast. Be in the target box early.

A 39°C+ airmass that finally breaks can deliver flash flooding on run-off-prone ground, large hail, frequent lightning and damaging outflow.

What to watch

Keep the Met Office warnings page open alongside our 5-day outlook. Live radar and the targets board will catch the first cells the moment they fire.

Until then: stay in the shade, drink more than you think you need, check on neighbours — and have the kit ready for when it breaks.