Temperatures are set to reach 30C (86F) in parts of the UK on Thursday, with the heat expected to build steadily as the week goes on.

It is likely to mean the first heatwave of 2025 being declared by the weekend. The nights will also be much warmer from Thursday, with many areas seeing temperatures in the high teens.

Temperatures will peak in different areas on different days, with some of the highest figures on Thursday expected in the south and east, the Midlands and South West England.

By Friday, the north and west will be feeling the heat, with Aviemore, Strabane and Aberystwyth among the possible spots to hit 28C or higher.

Northern Ireland, western Scotland and west Wales will see temperatures peak on Friday with highs of 24 to 28C likely.

For east Wales, eastern Scotland and much of England the peak will be on Saturday, where many areas will see highs of 28 to 31C, while some places in south-east England and East Anglia may reach 33C.

Saturday night could see the first “tropical night” of the year. This is where overnight temperatures do not drop below 20C, something that is increasingly likely for parts of south-east England.

The heat is down to a developing area of high pressure. This will help winds switch to a south-easterly direction and draw in hot weather from other parts of Western Europe. Parts of France and Spain could see temperatures close to 40C over the next few days.

For a heatwave to be declared by the Met Office we need to reach a threshold temperature for at least three consecutive days, and that threshold varies from 25C across the north and west of the UK, to 28C in parts of eastern England.

Whilst we have seen temperatures exceeding these figures in recent weeks, the warm spells have not been long enough to qualify as a heatwave – but that looks like it is about to change.

Meanwhile, a Met Office study said the risk of 40C temperatures in the UK was rapidly increasing.

The last time temperatures exceeded 40C in the UK was 19 July, 2022

Writing in the journal Weather meteorologists said there was a 50:50 risk of temperatures exceeding 40C in the UK in the next 12 years – four years earlier than the previous estimate, and that temperatures of 45C or more “may be possible”.

The UK’s June temperature record stands at 35.6C, set in Southampton in 1976. Current forecasts suggest this is unlikely to be exceeded this time.

That infamous summer included the longest continuous heatwave on record, with 18 days above 28C. However, the Met Office’s model found that today’s climate could support a heatwave lasting up to 39 days.

High pressure and rising temperatures have prompted the UK Health Security Agency (UKHSA) to issue yellow heat-health alerts for most of England from midday Wednesday to Sunday evening.

While yellow is the lowest level (below amber and red), it warns of possible impacts on health and social services and recommends preparation for vulnerable groups, including the elderly.

It is worth noting that heatwave conditions do not always mean sunshine. As temperatures rise over the weekend, showers or thunderstorms could develop across parts of the UK.

A quick check of the BBC Weather app will show when the risk of rain increases locally – useful for anyone planning to spend time outdoors.

Current UK forecasts are showing that winds will start to switch to less hot westerlies from Saturday onwards. However, it’s likely to be still very hot in eastern areas on Sunday with temperatures above 30C for some.

However, even next week with a greater chance of occasional rain, hotter weather will still not be far from the south-east corner of the country.