A new heatwave is starting to build across parts of the UK from this weekend, with forecasters warning that temperatures could reach 33C or 34C.

For some areas this will mark the third heatwave of the year.

It comes as week-long yellow heat health alerts have been issued by the UK Health Security Agency from the Midlands and East Anglia down across both the south-east and south-west of England.

The highest temperatures are expected in southern England and while maybe not as intense as the record-breaking heatwave in June, it may last a lot longer.

Temperatures in the south of the UK will continue to rise gradually over the weekend as high pressure builds from the Azores.

It will turn warmer still from Monday with the heat expected to peak during the second half of the week across England and Wales.

Some areas are likely to meet official heatwave criteria.

The highest temperatures will be focused across southern and eastern England, where values could widely exceed 30C.

In the north-east of England and eastern Scotland the mid to high-20s are possible.

Areas on the western side of the UK – such as Lancashire, the Lake District, western Scotland and Northern Ireland – will be exposed to an Atlantic breeze which will act like a natural air conditioner limiting temperatures to the low to mid-20s.

Currently many forecasting models show that the hot spell could persist into the middle of July.

We are unlikely to exceed the record breaking temperatures recorded in June, although there is some uncertainty.

Yellow heat health alerts have been issued by the UK Health Security Agency for the East Midlands, West Midlands, east of England, London, south-east England and south-west of England.

These came into force at 12:00 BST on Saturday and are valid until 20:00 on Saturday 11 July.

The alerts warn of an increased risk to health, particularly for vulnerable people, due to the expected heat.

In the UK, a heatwave is defined as a period of at least three consecutive days where daily maximum temperatures meet or exceed regional thresholds – which vary from 25 to 28C across the country.

During such conditions, there is an increased risk of heat-related illness, especially among older people and those with underlying health conditions.

A ridge of high pressure linked to the Azores High – a large semi-permanent centre of high atmospheric pressure – is expected to extend north-eastwards across the UK, while the jet stream shifts further north.

This will block the progress of Atlantic low-pressure systems, leading to a more settled weather pattern – bringing plenty of sunshine, dry weather and another notable burst of summer heat for many.